The authors review the available evidence regarding the nature, cause, and treatment of the premenstrual syndromes. They attribute the contradictory results of various studies and the current theoretical confusion in the area to the failure of investigators to carefully define the syndromes, formulate a set of answerable questions, and select a homogeneous population before initiating their studies. The relationship between premenstrual syndromes and major psychiatric disorders, as well as the clinical and theoretical relevance of the menstrual cycle to major psychiatric disorders, is discussed. The authors offer recommendations to both investigators and clinicians for more careful observation and documentation of the relationship between mood disorders and the menstrual cycle.