Paul Reilly
Analyst · Matt Sheerin, Stifel
Thanks, Mike. Fourth quarter sales of $6.75 billion grew 6% year-over-year. Sales adjusted for acquisitions and changes in foreign currencies grew 4% year-over-year. Overall, sales were above the high end of our prior guidance range. In global components, sales of $3.67 billion grew 6% year-over-year, adjusted for changes in foreign currencies. Adjusted for acquisitions and changes in foreign currencies, global components sales were approximately flat year-over-year.
In the Americas, sales declined 4% year-over-year. Americas core sales were flat with the third quarter. In Europe, sales adjusted for acquisitions and changes in foreign currencies increased significantly again this quarter, advancing 12% year-over-year, the fourth quarter in a row of double-digit constant currency growth. We experienced strength across the entire continent. Sequentially, core sales in Europe were down 3% year-over-year -- I'm sorry, down 3% quarter-over-quarter. Sales in Asia grew 6% year-over-year and declined 4% year-over-year, adjusted for acquisitions and changes in foreign currencies. Core sales in Asia grew 2% quarter-over-quarter, which was better than our expectations.
Global components fourth quarter book-to-bill was 1.05, which is above the 3 prior years' fourth quarter. Through the first 4 weeks of the first quarter, our book-to-bill remains above parity. Global components backlog also grew slightly in the fourth quarter, whereas we normally experience a sequential decline. We believe this suggests a solid foundation for our business as a whole in the short term. Fourth quarter enterprise computing solutions sales were $3.08 billion, up 10% year-over-year. For the full year 2015, ECS billings grew 9% year-over-year, adjusted for acquisitions and changes in foreign currencies. And ECS billings growth in the fourth quarter accelerated up to 11% year-over-year.
In the Americas, sales grew 11% year-over-year and grew 5% adjusted for acquisitions and changes in foreign currencies. Sales for our core ECS Americas distribution business grew 50% quarter-over-quarter and were above our expectations. In Europe, sales in constant currency advanced 22% year-over-year. And Europe ECS sales grew 76% quarter-over-quarter and hereto, were above our expectations. The better-than-expected performance in the fourth quarter ECS sales in both regions was principally attributable to even higher growth in security and infrastructure software off an already robust growth levels and, to a lesser extent, some server refresh activity.
Returning to consolidated results for the quarter. Our gross profit margin was 12.4%. Year-over-year, gross margins were down 30 basis points. The decline was principally attributable to greater relative contributions from ECS and Asia components within our mix. Total company operating expenses increased 4% year-over-year, as reported, and 3% year-over-year adjusted for the impact of acquisitions and changes in foreign currencies. Operating expenses decreased 20 basis points as a percentage of sales on a year-over-year basis.
Operating income was $284 million, a 7% increase year-over-year adjusted for changes in foreign currencies. Operating margin declined 20 basis points year-over-year due to acquisitions and a lower contribution from Americas components within our mix. Global components operating margin of 4.3% decreased 10 basis points year-over-year. Global enterprise computing solutions operating margin was 5.8%, hereto decreasing 10 basis points year-over-year in both businesses, principally driven by acquisitions. Our effective tax rate for the quarter was 27.2%. Net income was $182 million, up 6% year-over-year, adjusted for changes in foreign currencies. Earnings per share were $1.94 on a diluted basis and grew 3% year-over-year. Earnings per share grew 10% year-over-year, adjusted for changes in foreign currencies.
Cash flow from operations was $544 million for the fourth quarter of 2015. Full year 2015 cash flow from operations was $655 million or approximately 132% of our GAAP net income, well in excess of our goal to deliver cash flow at a rate of 70% of our GAAP net income. We expect normal seasonally lower cash flow in the first quarter. Consolidated return on working capital for the fourth quarter was 33%, and return on invested capital was 12.4%, generally outpacing our long-term weighted average cost of capital. We repurchased approximately $150 million of our stock in the fourth quarter, approximately $341 million over 2015 and approximately $1.4 billion over the last 5 years. And during the quarter, authorization remaining under our existing share repurchase program was $320 million. This is a high-level summary of our financial results. For more detail regarding the business unit results, please refer to the CFO commentary published this morning.
Now turning to guidance. We believe that total first quarter sales will be between $5.25 billion and $5.65 billion, with global components sales between $3.55 billion and $3.75 billion and global enterprise computing solutions sales between $1.7 billion and $1.9 billion. We expect earnings per share, on a diluted basis, excluding any charges, to be in the range of $1.34 to $1.46. Our guidance assumes an average tax rate in the range of 27% to 29%. Average diluted shares outstanding are expected to be 93 million. The average USD-to-euro exchange rate we are using for forecasting purposes is $1.10 to EUR 1.