Pioglitazone is a novel oral anti-diabetic agent belonging to the thiazolidinedione class. Pioglitazone has been shown to be effective and well tolerated in the treatment of patients with type 2 diabetes, as it reduces insulin resistance and improves glycaemic control and abnormal lipid profiles. This double-blind, randomised, placebo-controlled study was conducted for further evaluation of the efficacy and tolerability of once-daily administration of pioglitazone monotherapy alongside dietary measures in patients with type 2 diabetes. Following a 10-week washout period, 251 patients received one of three treatment regimens for 26 weeks: placebo + diet (n = 84), pioglitazone 15 mg once-daily + diet (n = 89), or pioglitazone 30 mg once-daily + diet (n = 78). Pioglitazone, both 15 and 30 mg/day, in addition to dietary control, was associated with significant reductions (vs. placebo) in mean levels of both glycosylated haemoglobin (HbA 1C ) and fasting blood glucose (FBG). HbA 1C was reduced by 0.92 % and 1.05 %, respectively, and FBG was reduced by 34.3 and 36.0 mg/dl, respectively, compared with the control group. Pioglitazone at 15 and 30 mg/day significantly reduced postprandial blood glucose levels at all visits (- 163 and - 165 mg/dl/hour, respectively) compared with an increase of 47.7 mg/dl/hour on placebo. The profile and frequency of adverse events were similar in all treatment groups. These results indicate that pioglitazone monotherapy together with dietary control is both effective and safe in patients with type 2 diabetes.