A central, reversible decrease in male sexual function appears related to some aspect of obstructive sleep apnoea (OSA). Lower serum testosterone (T) levels were documented in 15 men with OSA versus nine snorers (no OSA), (9.18 ± 0.92 vs 11.55 ± 0.90 nmol/l, mean ± SEM), P < 0.05 in a consecutive case series of 24 men referred for diagnostic overnight sleep studies. Gonadotrophins did not differ between the two groups. Although the men with OSA did not differ in body mass index (BMI) or weight from the snorers, they were older (51 ± 3.9 vs 44 ± 3.1 years), P < 0.02. Serum T did not correlate with age, but was correlated with minimum nocturnal arterial oxygen saturation (Min SaO2) (r=0.589), P < 0.02. A prospective controlled trial of uvulopalatopharyngo-plasty therapy (UPP) for OSA in 12 subsequent subjects showed reproductive improvement which was parallel with improved apnoea at 3 months post-surgery. T increased (13.31 ± 1.07 to 16.59 ± 0.72 nmol/l), P<0.02, without significant changes in BMI, serum PRL, LH or FSH. All seven of the men who reported decreased sexual interest prior to surgery felt their libido and sexual functioning had returned to normal 3 months following UPP. Some aspect of OSA in men appears to produce a reversible hypothalamic-pituitary reproductive dysfunction.