OBJECTIVES:  To evaluate insulin treatment patterns for new insulin users in the UK and to identify factors associated with patients initiating insulin glargine. METHODS:  A retrospective cohort study using Clinical Practice Research Datalink (CPRD) was conducted. Patients with type 2 diabetes mellitus (T2DM) (age ≥18 years) and type 1 diabetes mellitus (T1DM) (age ≥6 years) were included. The index period was the first insulin prescription from 2009-2013 and patients were followed for up to five year after insulin initiation. Logistic regressions were performed to identify factors associated with initiation of insulin glargine. RESULTS:  Of the 3030 T1DM patients identified, 37% initiated their insulin therapy with glargine, 21% with determir and 13% with NPH ; 88% had a prescription for rapid acting (prandial) insulin. At baseline, T1DM patients initiating insulin glargine had a mean age of 28 years, 60% male, mean body mass index (BMI) of 24.3 and mean haemoglobin A1c (HbA1c) at 10.9%. Of the 15,863 T2DM patients identified, 32% patients initiated their insulin therapy with glargine, 27% with insulin isophane (NPH) and 15% on determir ; 33% had a prescription for rapid acting (prandial) insulin. At baseline, T2DM patients initiating insulin glargine had a mean age of 65 years, 56% male, mean BMI of 30.7 and mean HbA1c at 9.7%. The anti-hyperglyacemic drugs commonly prescribed were metformin (78.5%), Sulfonylureas (81.6%), DPP-4 inhibitors (30.0%) and Thiazolidinediones (25.5%). Factors associated with glargine initiation among patients with T2DM included increased age, other anti-hyperglycaemic drugs and microvascular complications. CONCLUSIONS:  Among patients identified as new users of insulin in the UK between 2009 and 2013, 32% and 37% of patients with T2DM and T1DM, respectively, initiated their insulin therapy with glargine. Age, comorbidities and other anti-hyperglycaemic drugs, were among factors associated with glargine initiation in patients with T2DM.