Studies of compliance with pharmacologic treatment in patients with bipolar disorder have primarily involved outpatients receiving lithium. To date, very little data addresses the rates of noncompliance in patients with bipolar disorder treated with other available mood stabilizers (e.g. divalproex, carbamazepine). One hundred and forty patients initially hospitalized for a bipolar disorder, manic or mixed episode, were evaluated prospectively over 1 year to assess their compliance with pharmacotherapy. Compliance was assessed by a clinician-administered questionnaire, using information from the patient, treaters, and significant others. Seventy-one patients (51%) were partially or totally noncompliant with pharmacologic treatment during the 1-year followup period. Noncompliance was significantly associated with the presence of a comorbid substance use disorder. Denial of need was the most common reason cited for noncompliance. Compliance was associated with being male and Caucasian and with treatment with combined lithium and divalproex or with this combination and an antipsychotic. Noncompliance with pharmacotherapy remains a substantial problem in the treatment of patients with bipolar disorder.