Seventy women with prolactinomas, age 19-38 years, were studied in order to evaluate a possible relationship between the use of steroidal oral contraceptives (o.c.) and the development of prolactin-producing adenomas. Sixty-seven patients were admitted for investigation because of menstrual bleeding disturbances and three patients because of galactorrhea. Forty-three patients (61%) had used o.c. Thirty-six out of forty-three women (83%) experienced their menstrual disturbances and/or galactorrhea when using o.c. or immediately after discontinuing the pill. Patients who had used o.c. had shorter duration of symptoms, lower S-prolactin levels and less pronounced enlargement of the sella turcica. These tendencies indicate that o.c. lead to an earlier manifestation of clinically latent prolactin-producing tumours. With or without previous o.c., the patients showed a low total fertility rate, indicating a notably long, clinically undiagnosed period of disease. The accumulated usage of o.c. by the women with prolactinomas was not higher than among the total female population of the same age in Sweden. Furthermore, patients on o.c. for several years did not show a more advanced form of the disease than women who had not taken the pill. Thus, the present study provides no support for the hypothesis that o.c. promote the growth of prolactin-producing pituitary adenomas.