Higher rates of mental ill-health, particularly mood disorder, have been reported in women compared to men and this discrepancy has been attributed to underlying biological changes associated with the menstrual cycle. The literature relating to psychiatric ill-health and the premenstrual syndrome is, accordingly, critically evaluated and the evidence favouring a causal role for menstrual cycle changes in the genesis of such ill-health is briefly reviewed. A simple model of causation attributing psychiatric-ill-health to hormonal variation in the menstrual cycle is eschewed in favour of a multifactorial model which assumes an interaction between hormonal and hormonally-related changes in the premenstruum, basic personality and social dissatisfactions, adverse life circumstances, and interpersonal stresses.