OBJECTIVES: To investigate patterns and costs of self-monitoring of blood glucose, and its effect on glycaemic control, among insulin-using diabetic patients in Tayside, Scotland. METHODS: The population-based DARTS diabetes database was used to identify all insulin-using patients diagnosed with type 1 or type 2 diabetes prior to 1993. The numbers of glucose-monitoring test strips dispensed in 1993-1995 were determined from the MEMO dispensed prescribing database, and average costs per patient calculated. The effect of self-monitoring on glycaemic control was investigated in a linear regression model (with HbA1c as the outcome variable). Independent variables were numbers of strips dispensed in the 6 months prior to the HbA1c reading, age, sex and deprivation. RESULTS: Among 807 patients with type 1 diabetes, 15% obtained no test strips. 20% obtained enough strips to test glucose daily, and 1% four times daily. The corresponding figures for the 1,240 insulin-using patients with type 2 diabetes were 30% (no strips) and 12% (daily tests). Age and deprivation influenced strip uptake. Average costs / patient / year were £64.40 for type 1 diabetes and £44.80 for type 2 diabetes, compared with £409 for self-monitoring four times daily (recommended in the DCCT). For 258 patients with type 1 diabetes who had HbA1c values recorded, there was an association between strip uptake and glycaemic control (p <0.001), with an estimated decrease in HbA1c of 0.7% for every 180 test strips dispensed. There was no such association for 529 insulin-using patients with type 2 diabetes. CONCLUSIONS: Self-monitoring of blood glucose improves glycaemic control in type 1 diabetes, but a minority of patients self-monitor regularly. Costs are moderate compared with other costs of diabetes care.