A 25 year old man presented hypogonadotropic hypogonadism with complete anosmia (Kallman's syndrome). His chromosomic type was 47 XXY (Klinefelter's syndrome). Clinical findings were: height 183 cm, weight 62 kg, increased length of lower limbs, P2-A2 pilosity and micropenis. Only a left testis was present (1.5-1.5 cm). Bone age was 15. Testicular biopsy showed that the signs were more related to the gonadotropic deficit than to the gonadal dysgenesis; tubular hyalinization was not observed. Plasma levels of testosterone and oestradiol were very low. Plasma gonadotropin levels were below normal ranges and did not respond to an infusion test of GnRH. GnRH was administered iv every 90 min for 3 weeks by an auto syringe infusion pump and induced a pulsatile response of FSH and LH. Plasma levels of testosterone and oestradiol were unaffected. It may be concluded that the results of pulsatile injection of GnRH confirmed in this patient a unique association of Kallmann's syndrome with complete 47 XXY Klinefelter's syndrome.