In a WHO-co-ordinated prospective multi-centre study in Agra and Chandigarh (India), Cali (Colombia), Ibadan (Nigeria), Manila (Philippines) and Nottingham (UK), 926 women undergoing elective sterilization for fertility control and 924 controls using other methods of contraception, were examined before the operation and at entry into the study, respectively. Of the initial sample, 81·6% were re-examined at a 6-month follow-up and 77·4% at a 12-month follow-up. At initial examination, the prevalence of clinically significant emotional disorder ranged from 1·6% to 14·6% in four of the six centres; it was higher in Cali (25·5%) and nil in Ibadan. In all centres except Agra, women applying for sterilization had a somewhat higher rate of mental health problems than control subjects at initial examination. At the 6-month follow-up, the prevalence was within the range 1·6–15·4% for the sterilization group and 0–14·5% for the control group in all centres except Cali which continued to have a higher rate. At the 12-month follow-up the prevalence of mental ill-health ranged from 0% in Manila to 29·2% in Chandigarh; if the latter centre were removed, the range would be 0–13·6%. There were no significant differences in the frequency of mental ill-health between sterilization cases and control subjects in any of the centres. Further, there were no significant differences in the prevalence of mental ill-health in relation to the timing of sterilization, i.e. interval, post-partum or post-abortion. Chandigarh was the only centre which showed a consistent increase of the rates of psychological disorder over time; in all other centres the rates showed some fluctuations but no clear tendency either to increase or decrease. The data do not support a notion of a significant impact of sterilization on mental health of women.