The concept of premenstrual syndrome (PMS) is considered and found wanting. The problems which are presented under the heading of PMS, however, are important and need better understanding A three factor model to account for such problems is presented. The three factors are (i) menstruation, problems with which may influence mood and well being premenstrually as well as during menstruation; (ii) the timing factor, linked to the normal hormonal cycle and producing cyclical variability in certain aspects of central nervous system (CNS) function; and (iii) the vulnerability factor, which is not a function of the menstrual cycle, but which involves other characteristics which result in some women reacting to the first two factors adversely. Evidence is presented that the mood changes which commonly occur perimenstrually are linked to cycle-related alterations in serotonergic activity in the CNS, and premenstrual food craving may be a marker of such alterations. The term 'menstrual cycle related problems' is offered as a preferable alternative to 'premenstrual syndrome'.