Idiopathic hypogonadotrophic hypogonadism (IHH) is a potentially correctable cause of male infertility. However hormonal treatment is usually a slow process and artificial reproductive techniques such as intracytoplasmic sperm injection (ICSI) might be resorted to before full testicular response has been achieved. We report here an unusual variant of IHH of post-pubertal onset in which early intervention with ICSI was attempted. Our patient was 37 years old and presented with male infertility due to azoospermia and undetectable serum gonadotrophin concentrations. He had an apparently normal pubertal development, a testicular volume of 8 ml, normal pituitary-thyroid and pituitary-adrenal function, as well as normal computerized tomographic appearance of the sella region. A combination of human chorionic gonadotrophin (HCG) and menopausal gonadotrophins (HMG) was administered. Spermatozoa were first detected in the semen after 3 months and reached a concentration of approximately 2x10(6)/ml after 9 months. ICSI was attempted at this point; the spermatozoa had good fertilizing ability and three embryos were obtained and replaced. Unfortunately no pregnancy resulted. Treatment with 5000 IU HCG and 150 IU HMG three times per week was continued and sperm counts rose rapidly thereafter to reach 28.3x10(6)/ml after 16 months of injections. His wife conceived naturally during this period and the pregnancy is now in the second trimester. This case illustrates the good prognosis of the rare patient with IHH of post-pubertal onset when treated with gonadotrophins, and suggests that ICSI procedures should be delayed until final testicular maturation is attained.