Temperament and mood swings are promising indicator for the characterization of mood-spectrum vulnerability. The aim of this study was to investigate the relationship between affective temperament and mood swings in bipolar disorder. We explored these clinical features retrospectively. Patients who met the criteria for Bipolar I disorder were enrolled in the study. Exclusion criteria were partial remittance and a full affective or psychotic episode. Data concerning illness and family history, mood swings (semi-structured interview) and depression (BDI) were obtained. We examined premorbid temperament with TEMPS-A, and with the validated German version TEMPS-M. Patients with and without mood swings were compared with respect to the dominant temperament. Out of 20 bipolar patients, 6 subjects reported mood swings prior to the onset of affective disorder. Subjects with mood swings significantly correlated with a positive family history of affective disorders. Concerning cyclothymic, irritable, and hyperthymic temperament, bipolar affective patients with mood swings had higher scores. No differences were found between males and females. Our findings support the assumption that mood swings, as represented by the cyclothymic temperament, could be prodromes of bipolar disorder. These traits may represent vulnerability markers and could presumably be used to identify individuals at high risk for developing bipolar disorder in order to prevent this illness or to modify its course. A further retrospective study with a larger sample size was started to deepen knowledge about putative prodromal symptoms of bipolar disorder.