OBJECTIVES: The Quality and Outcomes Framework (QOF) was introduced in the UK in April 2004. The scheme financially rewards practices for providing quality care and this is evaluated based on electronic medical records. This study therefore evaluated whether data recording changed after QOF was introduced. METHODS: Patients were selected from The Health Improvement Network (THIN) database, which holds longitudinal anonymised primary care records from >450 UK practices. Patients were grouped according to whether they ever had ≥1 of 15 chronic QOF diseases. Percentages of patients with ≥1 general practice (GP) visit, smoking status, blood pressure (BP) and weight record were estimated throughout nine 12-month time periods (January 4, 2000-January 4, 2009). T-tests compared mean percentages before and after QOF introduction (January 4, 2004). RESULTS: Percentage of QOF patients ranged from 26.6% to 32.9% over time and non-QOF patients from 67.1% to 73.4%. The average percentage of QOF patients with a GP visit was 80.5% (standard deviation (SD):3.2) before QOF and 84.5% (SD:0.9) after QOF (p=0.086). These percentages were 57.5% (SD:3.5) and 62.0% (SD:0.6) (p=0.082) for non-QOF patients. The average percentages for smoking recording were 26.8% (SD:12.9) versus 55.9% (SD:3.0) (p=0.018) for QOF patients and 10.9% (SD:4.8%) versus 22.3% (SD:2.9) (p=0.010) for non-QOF patients. For BP recording, 53.6% (SD:6.7) versus 68.1% (SD:4.8) (p=0.013) for QOF patients and 20.5% (SD:2.9) versus 24.2% (SD:0.9) (p=0.084) for non-QOF patients. For weight recording, 25.5% (SD:5.4) versus 40.4% (SD:3.2) (p=0.006) for QOF patients and 9.8% (SD:1.7) versus 14.8% (SD:1.7) (p=0.004) for non-QOF patients. CONCLUSIONS: Overall, the proportion of GP visits and clinical recording increased after QOF was introduced, although there was no evidence of a difference for GP visits or BP in non-QOF patients. This suggests that QOF influenced recording, especially the recording of the evaluated clinical measures for patients with chronic QOF diseases.