OBJECTIVES:  To evaluate the general practitioners' (GPs) reasons for prescribing pioglitazone 15 or 30 mg and characterise the patients on these doses. METHODS:  An internet-based survey was conducted among 245 UK GPs who selected reasons for prescribing pioglitazone 15 or 30 mg/day for their patients.  Eligible patients were ≥18 years at type 2 diabetes mellitus (T2DM) diagnosis and currently on pioglitazone (15 or 30 mg) with other oral antihyperglycaemic agents for ≥3 months.  GPs provided clinical data for ≥1 patient on each pioglitazone dose.  The 29 potential reasons for prescribing the current pioglitazone dose were classified into 4 categories:  sufficient glycaemic control, poor tolerability and/or side effects associated with pioglitazone, comorbidity/polypharmacy, and patient-related factors. RESULTS:  Of the 1456 patients provided by GPs, 739 were on pioglitazone 15 mg and 717 on 30 mg.  Compared with the 30-mg group, patients in the 15-mg group had a shorter duration of T2DM (median 7.3 vs. 8.3 years) and the same median HbA1c level (7.2%).  Collectively, reasons in the sufficient glycaemic control category were selected most for both groups; however, they were selected more often for 15 than 30 mg (85 vs. 75%, p<0.0001).  Specifically, "new user" was selected for 26% on 15 mg and 11% on 30 mg (p<0.0001).  No significant differences between groups were seen within the other categories.  Overall, 37% of GPs selected reasons related to poor tolerability and/or side effects, 42% for comorbidity/polypharmacy, and 30% for patient-related factors.  GPs indicated they had no plans to change the current pioglitazone dose for 58% on 15 mg and 66% on 30 mg. CONCLUSIONS:  UK GPs in this study appear comfortable with their current pioglitazone dose choice for their patients and a majority of GPs planned to have their patients continue on their current pioglitazone dose in combination therapy.