This study compared the personality traits of subjects with bipolar I disorder in remission to the personality traits of subjects with no history of any mental illness. Subjects were assessed as part of a prospective, multicenter, naturalistic study of mood disorders. Diagnoses were rendered according to Research Diagnostic Criteria, through use of the Schedule for Affective Disorders and Schizophrenia - Lifetime Version. A total of 30 euthymic bipolar I subjects were compared to 974 never-ill subjects on 17 personality scales selected for their relevance to mood disorders. The subjects with bipolar I disorder in remission had more aberrant scores on 6 of the 17 personality measures, including Emotional Stability, Objectivity, Neuroticism, Ego Resiliency, Ego Control, and Hysterical Factor. These findings indicate that patients with bipolar I disorder in remission have personality traits that differ from those of normal controls.