The objective was to compare the efficacy and safety of adding low-dose rosiglitazone (2 or 4 mg/d) to insulin therapy vs continued insulin monotherapy in patients with type 2 diabetes mellitus who were unable to achieve glycemic control with insulin therapy alone.In this 24-week, double-blind study, 630 individuals with type 2 diabetes mellitus that was inadequately controlled with insulin therapy alone were randomized to treatment with rosiglitazone (2 or 4 mg/d) or placebo in combination with ongoing insulin therapy. The dosage of insulin therapy could be adjusted at the investigator's discretion if required for hypoglycemia or additional glycemic control.The addition of rosiglitazone (2 or 4 mg/d) to insulin therapy significantly decreased mean glycated hemoglobin concentrations compared with placebo plus insulin (-0.3% [P=.02] and -0.4% [P.001]) and compared with baseline (-0.6% and -0.8% [both P.001]) after 24 weeks. The addition of 2 or 4 mg/d of rosiglitazone significantly decreased the C-reactive protein level (vs baseline: -22.0% [P.001] and -34.2% [P.001]; vs placebo: -22.2% [P=.003] and -32.0% [P.001]) and fibrinogen (vs baseline: -10.5% and -12.0% [both P.001]; vs placebo: -7.9% [P=.002] and -7.6% [P=.004]), while 4 mg/d of rosiglitazone significantly reduced matrix metalloproteinase 9 levels (vs baseline: -17.1% [P=.007]; vs placebo: -23.3% [P.001]). The adverse event profile, including incidence of hypoglycemia and edema, was similar between treatment groups, and most adverse events were mild to moderate in intensity.The addition of low-dose rosiglitazone to insulin therapy is an effective and well-tolerated treatment option for patients with type 2 diabetes mellitus who continue to have poor glycemic control despite administration of exogenous insulin as monotherapy.clinicaltrials.gov Identifier: NCT00054782.