Aims: The aim of this analysis is to determine the timing of insulin initiation in routine clinical practice, especially in relation to glycaemic control and use of oral antidiabetic drugs (OADs). Methods: Study of Once Daily Levemir was a 24-week international observational study involving 10 countries which evaluated the safety and effectiveness of initiating once-daily insulin detemir in people with type 2 diabetes mellitus (T2DM) being treated with one or more OADs (clinical trial number NCT00825643 and NCT00740519). Results: A total of 17 374 participants were enrolled in the study: aged 62 +/- 12 years, 53% male, T2DM duration 10 +/- 7 years, body mass index 29.3 +/- 5.4 kg/m2. Pre-insulin HbA1c was 8.9 +/- 1.6%. The proportion of patients with HbA1c =9.0% ranged from 64% (UK) to 23% (Poland). Pre-insulin OAD treatment included metformin (81%), sulphonylureas (59%), glinides (16%), thiazolidinediones (TZD) (12%), a-glucosidase inhibitors (12%) and dipeptidyl peptidase (DPP)-IV inhibitors (7%). The mean starting dose of insulin detemir for the total cohort was 0.16 +/- 0.09 U/kg. Differences in OAD use and insulin doses at initiation were evident among participating countries. The largest proportional changes in OAD prescribing at insulin initiation were seen with glinides (+15%), sulphonylureas (-19%), TZD (-31%) and DPP-IV inhibitors (-28%). Conclusions: Despite well-documented benefits of timely glycaemic control and consensus guidelines encouraging earlier use of insulin, considerable clinical inertia exists with respect to initiating appropriate insulin therapy in people with T2DM. Considerable regional differences exist in the timing of insulin initiation and in the use of OADs.