Objective: To compare health care utilization and cost of children and adolescents with bipolar disorder treated with atypical antipsychotic (ATYP) versus with mood stabilizer (MS) monotherapy. Methods: We conducted a retrospective cohort study using Pharmetrics administrative claims data from January 1, 1998 to December 31, 2002. The study population included youths (6Results: After matching on the propensity score, 486 subject pairs were retained. On average, ATYP monotherapy subjects had fewer bipolar-related office visits (p=0.0041), but similar bipolar-related outpatient hospitalization (p=0.084), bipolar-related days of hospitalization (p=0.1707), and bipolar-related emergency department visits (p=1.00). ATYP monotherapy subjects had a lower cost of bipolar-related office visits (p=0.0246) but higher medication costs (p<0.0001). There were no cost differences between groups for bipolar-related emergency department visits (p=0.5477), bipolar-related outpatient hospitalization (p=0.9817), and bipolar-related inpatient hospitalizations (p=0.521). Total bipolar-related medical service (p=0.6501) and general health-related medical service (p=0.885) costs were also not significantly different between the two groups. Conclusion: Compared to patients with MS monotherapy, patients with ATYP monotherapy had fewer bipolar-related office visits and higher medication costs, but similar total bipolar-related and overall medical service costs.