We conducted a study on 91 women with thyroid cancer and 306 controls in hospital for acute nonneoplastic, non-hormone-related disorders in order to investigate the role of reproductive and hormonal factors in the etiology of epithelial thyroid cancer in the Canton of Vaud, Switzerland. Non-significant increases in cancer risk with an increasing number of full-term pregnancies (odds ratio, OR, after allowance for age and previous benign thyroid disease = 1.6, for > or = 3 vs. 0 full-term pregnancies, 95% confidence interval, CI: 0.7-3.6) and spontaneous abortions (OR = 2.0 for > or = 2 vs. 0 spontaneous abortions, 95% CI: 0.7-5.2) were seen. A significantly elevated OR (2.8, 95% CI: 1.1-7.2) was found in those women whose first pregnancy ended with an abortion. Whereas most other reproductive, menstrual and hormonal factors examined did not seem to affect the risk of thyroid cancer significantly, a clue emerged of an association between thyroid cancer and artificial menopause (OR = 6.3, for women who underwent artificial menopause vs. premenopausal women, 95% CI: 1.7-23.2). Although not necessarily causal, the relationship between the risk of epithelial thyroid cancer and the occurrence of spontaneous abortions and artificial menopause deserves attention in future studies, in the light of the high incidence of thyroid cancer in young and middle-aged women.