OBJECTIVE: To examine the effect of hypomanic states on maladaptive personality traits and personality disorders, the authors evaluated personality traits and disorders of patients during an episode of hypomania and after successful somatic treatment. METHOD: The authors used the Structured Interview for DSM-III Personality Disorders to study 66 outpatients who had a lifetime diagnosis of bipolar disorder and who met the minimum Research Diagnostic Criteria for hypomania. All patients had a knowledgeable informant separately undergo the Structured Interview for DSM-III Personality Disorders during the patient's hypomanic state. Outpatients who successfully recovered from the hypomanic episode (N = 47) and their informants were read- ministered the interview 4-8 weeks after the initial assessment. RESULTS: During the hypomanic state, informants generally reported higher levels of maladaptive personality traits among patients than patients themselves. For the patients who recovered successfully from the hypomanic episode, a reduction in all maladaptive personality traits except schizoid and dependent traits was reported by both patients and their informants; however, the decrease reported by patients generally was much greater than that reported by informants. In addition, schizoid traits actually increased after successful treatment according to patient reports but were unchanged according to informant reports. CONCLUSIONS: Hypomania may be associated with an exacerbation of maladaptive personality traits, which may be attenuated after successful treatment. Even with the attainment of euthymic mood, however, about 50% of the cohort had at least one personality disorder, which suggests that a high degree of comorbidity may exist between bipolar disorders and maladaptive personality traits or personality disorders.Abstract Teaser