Background: Good glycaemic control improves outcomes in patients with type 2 diabetes, but the extent to which this depends on adherence to insulin treatment is uncertain. Aim: To investigate the association between adherence to insulin and glycaemic control in insulintreated patients with type 2 diabetes. Design: Observational records-based study. Methods: We studied all patients with type 2 diabetes who were resident in Tayside, Scotland from 1 January 1995 to 30 September 2001, and who were treated with insulin. Adherence to insulin treatment was measured as the annual number of days of insulin coverage on the recommended dose, calculated from the amount of drug dispensed at community pharmacies and the recommended dose level for each patient. The association between glycaemic control (HbA1c), and adherence was determined, as was the influence of covariates, including age, sex, duration of diabetes and number of injections per day. Results: A total of 1099 people were studied: 574 (52%) males and 525 (48%) females, mean±SD age 62±12 years, diabetes duration 10-7 years. Median time in the study (time for which insulin was dispensed) was 1107 (range 366-2446) days.Ins ulin prescribed was 58.0±33.3 IU/day and insulin collected from pharmacies was 53.6±27.1 IU/day. Mean adherence to insulin was thus 70.6%±17.7%. Adherence to insulin (p=0.0021), BMI (p=0.0001) and diabetes duration (p=0.0314) were all significant predictors of HbA1c. Discussion: Adherence to insulin appears poor in these type 2 diabetes patients, and there was a significant relationship between adherence and long-term metabolic control.