OBJECTIVE: To determine the time that patients with type 1 and type 2 diabetes remain on their existing therapy whilst uncontrolled, before starting insulin or intensifying their insulin regimen. METHODS: A retrospective cohort study was conducted among subjects with type 1 and type 2 diabetes. A total of 154 clinical practices with continuous data over a 10-year period from 1st May 1995 until 30th April 2005 were included in this analysis. The study identified 9,979 individuals with type 1 diabetes (T1) and 62,533 individuals with type 2 diabetes (T2). Four patient groups were analysed: T1 on premix regimens; T2 prescribed ≥2 orals; T2 on basal regimen and T2 on premix regimens. The main study outcome was the median time to insulin initiation/ intensification in patients uncontrolled on their current therapy. RESULTS: The median time to intensification of insulin regimen for T1 patients uncontrolled on premix regimens, was 4.0 years (95% CI 3.2 to 5.4). The median time to initiation of insulin for T2 patients, prescribed two or more oral agents, with evidence of poor glycaemic control was 7.0 years (95% CI 6.5 to 7.7). Finally, the median time to intensification of the insulin regimen was 4.2 years (95% CI 3.5 to 6.1) for T2 patients uncontrolled on a basal regimen and > 8 years for those uncontrolled on a premix regimen. CONCLUSION: In spite of poor glycaemic control, insulin-naïve and insulin-treated patients fail to initiate/intensify insulin therapy for many years. Earlier initiation/ intensification of insulin therapy is likely to lead to better control and a reduction in the complications associated with diabetes. Barriers to insulin use must be overcome if patients are to achieve appropriate control.