It is widely accepted that the premenstrual phase of the menstrual cycle affects the mental health of some women. This article critically examines a potential tool that would enable further exploration of this subject. Incorporating qualitative and quantitative research, the author focuses on incident trends and service users’ experience of menstruation. The article concludes with a discussion about potential interventions that could support women in an inpatient setting whose mental health worsens during the premenstrual phase of their cycle.