AIMS: The aim of this retrospective cohort study was to estimate the time to insulin initiation in patients with Type 2 diabetes inadequately controlled on oral glucose-lowering agents (OGLAs). METHODS: Insulin-naive patients failing on OGLAs were identified from The Health Improvement Network database, which collects records from general practices throughout the UK. Patients were included if they were aged > or = 40 years, had concomitant prescriptions for > or = 2 OGLAs, and > or = 1 year of available records prior to the first occurrence of HbA(1c) > or = 8.0% after > or = 90 days of OGLA polytherapy at > or = 50% of maximum recommended dosages. RESULTS: A total of 2501 eligible patients with Type 2 diabetes who had an HbA(1c) above the OGLA failure threshold of > or = 8.0% were identified (54.0% male; 30.9% aged 60-69 years). It was estimated that if all the eligible patients were followed for 5 years, 25% would initiate insulin within 1.8 years of OGLA failure (95% CI 1.6-2.0), and 50% within 4.9 years (95% CI 4.6-5.8). The presence of diabetes-related complications had no substantial impact on the time to insulin initiation. CONCLUSIONS: This study found that 25% of patients with Type 2 diabetes had insulin initiation delayed for at least 1.8 years, and 50% of patients delayed starting insulin for almost 5 years after failure of glycaemic control with OGLA polytherapy, even in the presence of diabetes-related complications. Interventions that reduce this delay to insulin initiation are required to help achieve and maintain recommended glycaemic targets in patients with Type 2 diabetes.