Our guidance for diluted adjusted EPS was a range from $3.73 to $3.81, and we delivered $3.76 excluding restructuring but including net Q4 tax increase of $0.02 a share. We increased our guidance range twice during 2011 to reflect the improved operating performance, favorable foreign exchange rates and tax benefits.
Free cash flow was $391 million compared to guidance of about $400 million. We delivered solid achievement against our guidance for both Q4 in the full year of 2011.
Our Q4 sales were $610 million, a reported increase of 5% over last year's fourth quarter. In our last call, we indicated that we expected some market challenges in Q4 but fully expected to deliver full year organic sales growth in the mid-single-digit range. Our organic sales growth for the quarter, which excludes the impact of changes in foreign currency exchange rates and acquisitions, was 3%. After achieving 4% organic growth in research sales in each of 2011's first 3 quarters, our Research business grew 1% organically in Q4. Our SAFC business had its highest quarterly sales in Q4 2011 with organic growth of 7%. I'll have more comments on those increases shortly.
Acquisitions added 2%, while changes in foreign currency exchange rates had no impact on sales growth in the quarter compared to 2010's Q4.Our fourth quarter reported operating income was $160 million, a healthy 14% increase over 2010's adjusted Q4. Net income of $108 million was a 6% increase over last year's adjusted fourth quarter. Reported diluted EPS was $0.89, an adjusted gain of 7% over the prior year. Our Q4 free cash flow of $91 million was consistent with the amounts generated in both the fourth quarter of 2010 and in Q3 2011. Higher net income was largely offset by a higher level of working capital primarily due to planned inventory increases, which improved service levels to our customers in select market and slightly higher capital expenditures to support planned strategic growth initiatives.