This study assessed the single- and multiple-dose pharmacokinetics of 3 doses (15 mg, 30 mg, and 45 mg) of pioglitazone in 36 adolescents with type 2 diabetes. Blood samples were obtained over a 48-hour interval after the first dose (day 1) and over a 72-hour interval after the last dose (day 15) of pioglitazone and were assayed for pioglitazone and active metabolites (M-III and M-IV). Pioglitazone systemic exposure increased dose dependently but was less than dose proportional during multiple dosing. The median peak pioglitazone concentration occurred at 2 hours. The mean half-life was 8 to 9 hours for pioglitazone and 24 to 32 hours for M-III and M-IV, with similar values at each dose level. During multiple dosing, accumulation for pioglitazone was negligible, but it reached 2.5- to 3.0-fold for M-III and M-IV. The sustained total serum concentration of active compounds during multiple dosing provides the basis for once-daily dose administration of pioglitazone in adolescents.