This study examined the extent to which individuals with a lifetime diagnosis of recurrent unipolar disorder endorse experiencing manic/hypomanic symptoms over their lifetimes and compared their reports with those of patients with bipolar I disorder.The study group included 117 patients with remitted recurrent unipolar depression and 106 with bipolar I. Subjects had their clinical diagnosis confirmed by the Mini International Neuropsychiatric Interview and were administered the Structured Clinical Interview for the Mood Spectrum, which assesses lifetime symptoms, traits, and lifestyles that characterize threshold and subthreshold mood episodes as well as "temperamental" features related to mood dysregulation.The patients with recurrent unipolar depression endorsed experiencing a substantial number of manic/hypomanic symptoms over their lifetimes. In both patients with recurrent unipolar depression and patients with bipolar I disorder, the number of manic/hypomanic items endorsed was related to the number of depressive items endorsed. In the group with recurrent unipolar depression, the number of manic/hypomanic items was related to an increased likelihood of endorsing paranoid and delusional thoughts and suicidal ideation. In the bipolar I group, the number of lifetime manic/hypomanic items was related to suicidal ideation and just one indicator of psychosis.The presence of a significant number of manic/hypomanic items in patients with recurrent unipolar depression seems to challenge the traditional unipolar-bipolar dichotomy and bridge the gap between these two categories of mood disorders. The authors argue that their mood spectrum approach is useful in making a more accurate diagnostic evaluation in patients with mood disorders.