OBJECTIVE To assess the incidence of testicular atrophy by evaluation of hormonal status, testicular histology and sperm production in chronic lepromatous patients. METHODS Forty-one male patients with a mean age of 39.5 years (range 16-57) were studied at the Leprosy Hospital, Istanbul, Turkey, and were compared with 15 age-matched controls with proven fertility. RESULTS Reduced testicular size was observed in 51% and gynaecomastia in 27%. Of the 31 patients who were married, 15 were primarily or secondarily infertile. Twelve of 16 patients had oligospermia or azoospermia. The mean basal luteinizing hormone (LH), follicle stimulating hormone (FSH) and oestradiol levels were significantly elevated and the level of testosterone significantly reduced when compared with the control group. CONCLUSIONS Whenever leprosy is diagnosed patients should be informed of the need for treatment of an acute attack and the need for routine assessment of FSH, LH, testosterone and oestradiol levels to detect hypogonadism and potential infertility.