BACKGROUND Administration of testosterone or dehydroepiandrosterone to subjects with low levels of these hormones was found to reduce thyroid antibody titres. Male-pattern baldness is accompanied by mildly increased androgen levels. The present study was aimed at investigating whether early-onset androgenetic alopecia determines the impact of exogenous levothyroxine on thyroid autoimmunity and hypothalamic-pituitary-thyroid axis activity in young men with autoimmune hypothyroidism. METHODS The study included 2 thyroid-antibody-matched groups of men with autoimmune hypothyroidism: subjects with early-onset androgenetic alopecia (group 1; n = 24) and subjects with no evidence of hair loss (group 2; n = 24). All patients were treated with exogenous levothyroxine. Circulating titres of thyroid peroxidase and thyroglobulin antibodies, as well as levels of thyrotropin, free thyroxine, free triiodothyronine, prolactin, total testosterone, calculated bioavailable testosterone, dehydroepiandrosterone-sulphate, and oestradiol were measured before levothyroxine treatment and 6 months later. RESULTS In both study groups, levothyroxine decreased thyroid antibody titres, reduced thyrotropin levels and increased free thyroid hormone levels. However, these effects were less pronounced in the men with early-onset male-pattern baldness than in the control men. The degree of reduction in antibody titres and thyrotropin levels correlated with baseline levels of total and calculated bioavailable testosterone, as well with baseline insulin sensitivity and treatment-induced improvement in insulin sensitivity. Concentrations of the remaining variables remained unchanged throughout the study period. CONCLUSIONS The results of the current study suggest that the benefits of levothyroxine therapy in men with autoimmune hypothyroidism are less pronounced in individuals with early-onset androgenetic alopecia.