Background: This analysis was designed to assess the efficacy and safety of aripiprazole compared with placebo in subpopulations of patients with acute manic or mixed episodes of bipolar I disorder. Methods: Acutely manic patients experiencing DSM-IV manic/mixed episodes of bipolar I disorder were pooled from two randomized, three-week, flexible-dose, double-blind, placebo-controlled trials (N=516) and stratified by disease severity (Young Mania Rating Scale, YMRS), episode type, presence or absence of psychotic features, episode frequency, age, gender, and baseline severity of depressive symptoms. Safety and treatment-emergent adverse-event analyses were also performed. Results: Aripiprazole significantly reduced mean YMRS total scores at end point compared with placebo in patients with more or less severe illness, with mixed or manic episodes, with or without psychotic features, or with a history of rapid or non-rapid cycling (p < 0.01 for each subpopulation); in men and women (p = 0.001 for both); in patients in the 18-40 and 41-55 year e severity of depressive symptoms using the age groups (p <= 0.001 for both); and in three subgroups stratified by baselin Montgomery-Asberg Depression Rating Scale (p < 0.05). The treatment-emergent adverse events reported in >= 5% of patients aged 18-40 years receiving aripiprazole were similar to those reported for the overall population. Limitations: This post hoe analysis utilized pooled data from two short-term studies. Conclusion: Efficacy of the second-generation antipsychotic aripiprazole was noted across a broad range of subpopulations often associated with treatment resistance in patients experiencing manic or mixed episodes of bipolar I disorder. (C) 2007 Elsevier B.V. All rights reserved.