Objective: Temperament and personality in bipolar-I (BP-I) patients have been studied but temperament and personality in BP-I patients comorbid with adult attention deficit hyperactivity disorder (ADHD) have not been studied before. The aim of this study was to determine the effect of ADHD on the temperament and personality of BP-I patients in remission. Methods: Patients with a BP-I disorder diagnosis (n=121, female 71, male 50) were matched with control group with no known psychiatric illness (n=100, female 55, male 45) according to age, sex, education were recruited from consecutive admissions. After the sociodemographic form, SCID-I for childhood and adult ADHD and the other axis-I diagnoses according to DSM-IV criteria and SCID-II have been applied to all patients and control group. All patients were interviewed for the presence and history of current adult and childhood ADHD diagnosis. The subjects also completed the Adult ADD/ADHD DSM-IV Based Diagnostic and Screening Rating Scale Turkish version and the Turkish version of TEMPS-A Scale. Results: Adult ADHD diagnosis were observed in bipolar I patients with 21.7% (n=26) and in control group with 7% (n=7). Tempera-ment measurements revealed depressive type was found more commonly in the pure BP-I and the comorbid BP-I with adult ADHD group compared to the pure control group. There was no severe depressive temperament in the pure control group. When BP-I and the comorbid BP-I with adult ADHD group were analysed separately for the depressive temperament, there were no difference between the pure BP-I and the comorbid BP-I with adult ADHD group. The the comorbid BP-I with adult ADHD group were observed to have moderate/severe episodes, earlier and longer maintenance treatment periods. All three groups differ in terms of personality disorder. Antisocial personality disorder and schizotypal personality disorder were observed only in the comorbid BP-I with adult ADHD group. Conclusion: BP-I disorder comorbid with adult ADHD has significant clinical implications which may relate to a personality disorder. This may be due to the influence of ADHD on BP-I disorder.