Objective: To assess the efficacy of topiramate monotherapy for acute mania in children and adolescents with bipolar disorder type 1. Method: This double-blind, placebo-controlled study was discontinued early when adult mania trials with topiramate failed to show efficacy. Efficacy end points included the Young Mania Rating Scale (YMRS), Brief Psychiatric Rating Scale for Children, Children's Depression Rating Scale, Children's Global Assessment Scale, and Clinical Global Impressions-Improvement. Results: Fifty-six children and adolescents (6-17 years) with a diagnosis of bipolar disorder type I received topiramate (n = 29, 52%) or placebo (n = 27, 48%). The only statistically significant differences in efficacy measures between treatment groups were the difference between slopes of the linear mean profiles of the YMRS (p = .003) using a post hoc repeated measures regression and the change in Brief Psychiatric Rating Scale for Children at day 28 (-14.9 versus -.9, p = .048) using observed data. Adverse events with topiramate included decreased appetite, nausea, diarrhea, and paresthesia. Conclusions: Topiramate was well tolerated; however, the results are inconclusive because of premature termination resulting in a limited sample size. Adequately powered controlled trials are necessary to determine whether topiramate has efficacy in reducing symptoms of acute mania in children and adolescents. J. Am. Acad. Child Adolesc. Psychiatry, 2005;44(6):539-547. Key Words: mania, bipolar disorder, topiramate.