We investigated whether women diagnosed with comorbid bipolar disorder (BD) and premenstrual dysphoric disorder (PMDD) experience higher disruptions in biological rhythms in two independent study samples. The first study has a population-based sample of 727 women, including 104 women with PMDD only, 43 women with BD only, 24 women with comorbid PMDD and BD, and 556 women without BD or PMDD (controls). Biological rhythm disruptions were cross-sectionally evaluated using the Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN). The second study enrolled 77 outpatient women who completed prospective assessments at two timepoints: during the mid-follicular and the late-luteal phases of their menstrual cycles, using the BRIAN, and included 19 women with PMDD, 16 with BD, 17 with comorbid PMDD and BD, and 25 controls. In the population-based sample, all the diagnostic groups (BD, PMDD, BDPMDD) presented greater biological rhythm disruption than controls. In addition, women with BD presented greater overall biological rhythms disruption, and greater disruption in sleep, activity, and eating patterns, than women with PMDD. In the outpatient sample study, women with BDPMDD showed greater disruption in the social domain than women with PMDD. In the outpatient sample, women with BDPMDD reported significantly higher disruptions in biological rhythms across both the follicular and the luteal phases of the menstrual cycle. The comorbidity between BD and PMDD may affect biological rhythms beyond the luteal phase of the menstrual cycle. These results support previous literature on the increased illness burden of women diagnosed with comorbid BD and PMDD.