Objective: The aim of the present study was to investigate the relationship between affective temperaments and clinical features in bipolar disorder. Testing the relationships between phenomenological features, course, severity of episodes, overall severity of illness and comorbid conditions would clarify the reliability and validity of affective temperamental descriptions. Methods: One hundred patients with bipolar I disorder were recruited from consecutive admissions and evaluated when euthymic. Affective temperaments were assessed with TEMPS-A Turkish version. Information about the characteristics of each patient’s illness was obtained from three main sources; interview with patient (SCID-I), interview with at least one close relative and patient records. We compared the clinical features of patients with and without a specific affective temperament. Results: Similar rates of cyclothymic, hyperthymic and irritable temperaments were observed in bipolar patients. Five important findings of the present study were (1) hyperthymic temperament was more frequent in males than females; (2) manic switches were more frequent among bipolar patients with hyperthymic temperament; (3) psychotic features were more common in the irritable temperament group; (4) comorbid conditions, (mostly alcohol use disorders) were more common among bipolar patients with cyclothymic temperament; and (5) bipolar patients with irritable temperament were more likely to have a manic episode at the onset of illness. Conclusion: These findings suggest that affective temperaments have significant clinical implications in bipolar disorder, beyond the genetic basis and predisposing factors. There were significant differences between patients with different affective temperaments in terms of gender, type of first episode, psychotic symptoms, switch and comorbidity.