Several endocrine and sexual disturbances have been demonstrated in multiple sclerosis (MS) patients of both sexes. The endocrine profile, hypothalamic–pituitary–testis (HPT) axis and semen quality were evaluated in male patients with MS. A total of 68 male MS patients aged 18 years or older were recruited. Forty-eight age-matched healthy male volunteers served as controls. All subjects underwent complete physical examination and routine semen analysis. Two blood samples were drawn from each participant at 15-min intervals for the determination of the resting levels of: luteinising-hormone (LH), follicle-stimulating hormone (FSH), prolactin, testosterone, oestradiol and sex hormone binding globulin. The HPT axis was assessed using gonadotrophin-releasing hormone (GnRH) and human chorionic gonadotrophin tests. The mean basal serum levels for LH, FSH and testosterone in MS patients were significantly lower than the mean for normal controls (P = 0.01). The injection of GnRH analogue did not yield a significant increase in FSH and LH levels in the MS patients compared to normal controls (P = 0.001). Total sperm count, sperm motility and percent normal sperm morphology were lower in MS patients compared to controls. MS subjects with progressive disease had higher and more severe HPT axis abnormalities than that for patients with relapsing remitting MS. Most subjects with MS have hypogonadotrophic hypogonadism state and fertility impairment. It appears that the damage to HPT axis is both in pituitary and testicular levels. Further studies are needed to better elucidate the underlying pathophysiology of HPT axis dysregulation.