IntroductionHypothyroidism is a common disorder, appearing mainly in women although less frequently found in women with polycystic ovary syndrome (PCOS). The objective was to test the hypothesis that hyperandrogenism might protect against hypothyroidism. Material and methodsThe data from three prospective follow-up studies (up to 21years) and one register study were compared: women with PCOS (Rotterdam criteria), n=25, women with Turner syndrome, n=217, a random population sample of women, n=315, and men, n=95 (the WHO MONICA study). Findings were to be verified or rejected in all females, n=553 716, from the same region. The proportion of hypothyroidism was calculated and thyroid peroxidase antibodies (TPO) in serum were measured. ResultsHypothyroidism at >50years of age was found in 8% of women with PCOS, 4% in men (PCOS vs. men; ns), 43% of women with Turner syndrome, irrespective of karyotype (p<0.001 vs. PCOS), and in 17% of postmenopausal women in the population (p25years (5.5%) than in women without PCOS (6.8%) from the same region (p<0.01). ConclusionsHypothyroidism was less frequently seen in women with PCOS and in men compared with women in the general population and among women with Turner syndrome. This was not explained by altered autoimmunity or the Y-chromosome. Androgens seem to protect against hypothyroidism.