Ninety-two women with systemic lupus erythematosus treated with oral cyclophosphamide were studied to ascertain the prevalence and the factors associated with ovarian dysfunction. Menstrual disturbance during treatment occurred in 55% of patients: 36% had amenorrhoea and 19% had oligomenorrhoea. Sustained oligomenorrhoea occurred in 12% patients. Permanent amenorrhoea (> 12 months) after cessation of oral cyclophosphamide occurred in 27% of patients. Hormonal studies in these patients were consistent with ovarian failure. Older age at initiation of treatment and high cumulative dose of cyclophosphamide were found to be associated with this outcome. There was a trend towards linear relationship between the age of initiation of cyclophosphamide therapy and frequency of amenorrhoea. A statistically significant association between amenorrhoea and cumulative dose of cyclophosphamide after adjustment for age was found whereas no such association was linked to the duration of treatment. Fourteen of the 23 women who wished to become pregnant after cessation of treatment conceived resulting in 20 live births and two abortions.