OBJECTIVE: To measure whether more rapid transition toward insulin therapy in newly diagnosed Type II diabetic patients improves blood glucose control (BGC) and reduces risk of diabetic related complications (DC). METHODS: We used longitudinal data obtained from IMS Mediplus UK to identify patients newly diagnosed with Type II diabetes between November 1, 1993 and October 31, 1994. Newly diagnosed was defined as no prior diagnosis or use of antidiabetic agents. Patient data for five years included demography, laboratory values (Hb1Ac), treatment, DC and comorbidities. Patients were assigned to an initial treatment modality including diet and exercise (DE), sulfonylureas (S), antihyperglycemics (A), a combination (C), insulin (I), or insulin plus an oral agent (IO). Each stepwise transition in treatment, Hb1Ac readings and manifestations of DC were tracked for at least five years. Generalized Estimating Equations (GEE) estimated the expected reduction in Hb1Ac as patients transitioned to insulin sooner while controlling for baseline Hb1Ac and initial treatment assignment. Logistic regression was used to estimate the change in risk of DC associated with reductions in Hb1Ac and accelerated transitioning toward insulin treatment. RESULTS: 2,137 patients were eligible for analysis. By initial treatment patients were allocated as follows:1,894 (DE), 200 (S), 30 (A), 10 (C), 3 (I), and 0 (IO). Stepwise patients transitioned toward insulin with 180 patients by year 5. A total of 49 patients (2.3%) had at least one DC after controlling for baseline. Hb1Ac was reduced by 0.0037 (p=0.001) for each day sooner the patient was transitioned toward insulin therapy or a reduction of 1.0 in Hb1Ac (12.5%) can be expected if transitioned within 270 days. Logistic results indicated that transitioning toward insulin therapy by day 270 yields a reduction in risk of DC of 0.388% (p=0.01). CONCLUSION: Sooner transitioning to insulin therapy improves BGC and reduces the risk of complications.