Background: This 24-week Phase 3 double-blind placebo-controlled study assessed the safety and efficacy of dapagliflozin as add-on to insulin, with or without oral antihyperglycemic drugs (OADs), in Asian patients with inadequately controlled type 2 diabetes mellitus. Methods: Adult patients with HbA1c between >= 7.5% and <= 10.5%, body mass index <= 45 kg/m(2), and on insulin doses >= 20 IU daily were randomized to dapagliflozin 10 mg (n = 139) or placebo (n = 133) to assess 24-week changes in HbA1c (primary outcome), fasting plasma glucose (FPG), body weight, total daily dose of insulin (TDDI), and seated systolic blood pressure (SeSBP; exploratory outcome). Results: Baseline characteristics were similar in both groups. At Week 24, compared with placebo, dapagliflozin significantly improved HbA1c (mean [95% confidence interval] 0.03% [-0.11, 0.17] for placebo vs -0.87% [-1.00, -0.74] for dapagliflozin; between-group difference - 0.90% [-1.09, -0.71], P < 0.0001]), FPG, body weight, TDDI, and SeSBP. The incidence of adverse events (AEs) in the dapagliflozin and placebo groups was 80.5% and 71.2%, respectively, with few patients discontinuing due to AEs (dapagliflozin, 2.2%; placebo, 4.2%). The occurrence of hypoglycemia was similar in the dapagliflozin and placebo groups (23.7% and 22.6%, respectively; no major events). The frequency of urinary tract and genital infections was low; no deaths were reported. Conclusions: Dapagliflozin as add-on to insulin, with or without OADs, significantly improved glycemic control and reduced body weight and blood pressure in Asian patients. Dapagliflozin was well tolerated, with a similar frequency of hypoglycemia in both groups. These results support the use of dapagliflozin as add-on to insulin, with or without OADs, in this population.