There is circumstantial evidence that reproductive events can influence symptom severity of obsessive–compulsive disorder (OCD). We sent self-report questionnaires to 350 female outpatients with OCD to examine the relationship between the menstrual cycle, pregnancy, menopause, hormonal contraceptives, selective serotonin reuptake inhibitors and symptom severity of OCD. Yale–Brown Obsessive–Compulsive Scale scores were used at three serial time points during the menstrual cycle to assess symptom severity. One hundred and one out of 350 questionnaires (29%) were returned and completed. Forty-nine patients reported an exacerbation of OCD symptoms during the premenstrual period, nine during the menopause and 17 patients during pregnancy, whereas 11 patients mentioned improvement of OCD symptoms during pregnancy. Premenstrual dysphoric disorder could only partly explain a premenstrual exacerbation of OCD symptoms. Exacerbation of OCD could be related to reproductive events in a considerable number of patients, especially the premenstruum. Because reproductive cycle events influence the symptom severity of OCD, the menstrual cycle should be taken into account when assessing the severity of OCD symptoms during pharmacological studies.