Evidence from both retrospective and prospective studies suggests that many women do show cyclical changes in affect. Negative changes such as irritability, headache, tension, anxiety, sleep disturbance and depression are more frequent in the premenstrual and menstrual phases. Positive changes, pleasantness, increased vigour and elation are reported more often in the follicular or mid-cycle phases. Various theories have been suggested to explain these changes. These include psychodynamic, sociological and biological explanations. Although there is some evidence to support each theory no definite conclusions can be reached about the aetiological basis of most affective changes. Interpretation of studies attempting to link hormonal and affective fluctuations in limited by the many methodological problems outlined. Only one study appeared able to conclusively demonstrate a hormonal basis for a cyclical symptom. Suggestions are made for further research in this area.