In this study we sought to determine whether intracytoplasmic sperm injection (ICSI) could improve the efficacy of treatment with gonadotrophins in gonadotrophin-deficient men in terms of pregnancy. A series of six adult men (aged 26-47 years) with hypogonadotrophic hypogonadism (HH) is reported: four men with prepubertal isolated idiopathic HH (IIHH) and two adult-onset HH, as part of hypopituitarism secondary to surgical treatment of a pituitary tumour. All were azoospermic. To restore spermatogenesis, all received hormonal treatment with intramuscular human menopausal gonadotrophins (HMG) and human chorionic gonadotrophin (HCG) for 2 to 23 months. High basal serum inhibin B was predictive of rapid and complete recovery of spermatogenesis. In the two adult-onset HH, a natural pregnancy was achieved within 3 months. The four men with IIHH underwent ICSI because of poor sperm quality. ICSI using fresh or frozen-thawed ejaculated spermatozoa was performed after 6-23 months of gonadotrophin treatment. ICSI provided good clinical results in terms of fertilization and embryo quality, and resulted in three pregnancies that ended in three term deliveries. In men with oligozoospermia related to prepubertal IIHH, ICSI shortens the hormonal treatment and enhances the chances of pregnancy.