Rumination and mindfulness are transdiagnostic risk and protective factors while their role in Premenstrual Dysphoric Disorder (PMDD) is unclear. Thus, we aimed to investigate the cycle-phase-specific effects of rumination and mindful self-focus on momentary mood and cognitions in women with and without PMDD. This study involved brief ambulatory inductions of ruminative and mindful self-focus along with ambulatory assessments of negative (NA) and positive affect (PA), and rumination, present-moment-awareness (PMA) and self-acceptance on two days during both the follicular and late luteal phase in women with and without PMDD (n = 60 each). Compared to healthy controls, women with PMDD showed stronger increases in PA in response to mindful self-focus inductions during the late luteal phase, whereas no such group differences were identified during the follicular phase. Independent of clinical status and cycle phase, induced ruminative self-focus immediately increased momentary NA and rumination and decreased PMA, whereas induced mindful self-focus inductions increased momentary self-acceptance. Overall, higher PA-reactivity toward mindful self-focusing during late luteal phase in women with PMDD points to the potential of cycle-phase-specific mindfulness interventions for PMDD. Irrespective of cycle phase, rumination and mindfulness appear to represent targets for brief prevention and intervention measures for both non-clinical and clinical groups.