Thank you very much, Eilif. Before running through the results, I want to remind investors of 2 factors that impact our quarterly performance. First is seasonality. Higher education is a seasonal business. The third quarter represents the primary intake cycle for Mexico, a Northern Hemisphere market, and a smaller intake cycle for Peru, which is a Southern Hemisphere market.
Second, as you may recall from our discussion last quarter, last year, due to the COVID-19 pandemic, the start of certain classes in Peru were pushed to the second quarter of 2020. This timing difference skews year-over-year comparability for our performance and resulted in approximately $18 million more of revenue and related earnings recognized in the first half of 2021 versus prior year. This begins to reverse itself in Q3 this year, resulting in approximately $11 million less of revenue and related earnings with the remainder reversing in Q4.
Let's now move on to the strong financial performance for the third quarter, which we are very pleased with, starting on Page 12. Revenue in the third quarter was $268 million, and adjusted EBITDA was $76 million. Revenue and adjusted EBITDA were both ahead of the guidance that we provided 3 months ago. The majority of the outperformance was related to the growth momentum in the business, coupled with continued tight cost controls. As a result, we are increasing our full year guidance for 2021. In addition, during the third quarter, we expected to incur certain costs associated with readying our campuses for a return to face-to-face operations this semester. Those costs have been pushed to the fourth quarter as we now expect the return to campus operations in early 2022.
On a comparable basis, in a constant currency, revenue and adjusted EBITDA for the third quarter were up 13% and 68%, respectively. Adjusted for academic calendar impact, still on a comparable basis and at constant currency, revenue for the third quarter of 2021 was up 17% versus prior year and adjusted EBITDA increased by 84%.
The strong revenue performance in the quarter was led by Peru which experienced 20% year-over-year growth in revenue. The favorable results in Peru were driven by strong cycle 1 and cycle 2 intakes and significantly improved retention, driving total enrollment growth of 30% year-over-year. Mexico revenue for the third quarter increased 3% versus prior year, reversing the negative trends we experienced during the first half of the year. We expect that positive trend to continue in the coming quarters following the favorable primary intake just completed in that market.
Moving now to our year-to-date September results. When combined with the first half results, still on a comparable basis and at constant currency, our overall performance through year-to-date September resulted in revenue growth of 9% and an adjusted EBITDA increase of 89%. Adjusted for academic caliber impacts, still on a comparable basis and at constant currency, revenue for the 9 months of 2021 was up 8% versus prior year, and adjusted EBITDA increased by 79%, driven by strong operational performance and corporate G&A efficiencies.
Let me now provide some additional color on the performance of Mexico and Peru, starting with Page 15. Please note that all comparisons versus prior year are on organic and constant currency basis. Let's start with Mexico. Mexico just completed its primary intake for the year and results were very strong. New enrollments were up 11% during the intake and through September versus prior year. As a reference point, Mexico's September year-to-date new enrollment performance is up 4% versus pre-pandemic year-to-date September 2019, validating that with this intake complete, we have now come through the trough period in Mexico. The strong new enrollment intake, combined with a 4-point improvement in retention, resulted in total enrollment growth of 6% versus the prior period. This is up from the 1% increase we reported last quarter. Revenue for the quarter was up 3% as a result of higher enrollment volumes partially offset by carryforward impacts from increased levels of discounts and scholarships required during the pandemic.
Increased levels of discounting began in Q3 of 2020 and continued through much of the pandemic. We are now starting to see that abate during our large C3 intake that we just experienced and are focused on continuing to optimize on a go-forward basis. We do expect to see the carryforward effect of those discounts to impact our revenue for the coming quarters as those cohorts move through the system and we move to a more normalized level.
Finally, adjusted EBITDA was up 61% year-over-year for the quarter on a comparable basis, resulting from revenue growth and timing of expenses.
Let's now transition to Peru on Slide 16. For the smaller secondary intake, which occurred during the third quarter, new enrollments continue to trend favorably with an increase of 35% versus the same period prior year. Through the first 9 months of the year, new enrollments in Peru were up an impressive 20% versus prior year, and as a reference, are 9% ahead of pre-pandemic year-to-date September 2019 levels. Total enrollments increased 30% versus prior year, driven by the strong intake plus a double-digit improvement in retention rates as we have seen many students who dropped out last year when the pandemic began are returning to their studies.
Revenue for the quarter increased 20% on a constant currency basis, driven by the enrollment increase. Adjusted EBITDA of $71 million for the quarter was up 45% as compared to the third quarter of 2020. The increase year-over-year resulted from the strong enrollment intake and improved retention. Please note that year-to-date September revenue adjusted EBITDA were favorably impacted by the academic calendar timing discussed earlier. Year-to-date results adjusted for timing were up 22% and 65%, respectively.
Let me now briefly discuss our balance sheet position illustrated on Page 17. As of September 30, we were in a net cash position of $1.7 billion and total shares outstanding were approximately 181 million shares. During the third quarter, we completed the sale of Walden University, which drove the large cash balance at quarter end. Following the sale of Walden, on October 29, we distributed approximately $1.3 billion of cash to shareholders or $7.01 a share. The cash and debt balances as of September 30, 2021, are prior to the approximately $170 million in estimated taxes and fees due on prior sales, including Walden University, and approximately $158 million related to the expected release of a letter of credit and escrow account, both related to the sale of Walden University. We expect that the majority of the taxes and fees will be paid during the fourth quarter of 2021 and the letter of credit and escrow amounts will be realized in 2022. Our net cash position adjusted for those items is approximately $410 million at quarter end.
Now let's move to guidance, starting on Page 19. On the strength of our first 9 months of results and the positive growth momentum following our recent intake period, Laureate is increasing its full year 2021 guidance at the midpoint by 35,000 total enrollments, $35 million for revenue and $40 million for adjusted EBITDA. For continuing operations in 2021, our updated full year guidance is as follows: total enrollments are estimated to be approximately 385,000 students. Revenues are estimated to be between $1.075 billion and $1.085 billion. And adjusted EBITDA is SMB between $247 million and $253 million.
Eilif, with that, that concludes my remarks. I'm handing it back to you for closing comments.