OBJECTIVE: To assess the effect on spermatogenesis of adding recombinant follicle-stimulating hormone (FSH) to human chorionic gonadotropin (hCG) treatment protocols for adolescent/young adult males with hypogonadotropic hypogonadism (HH). DESIGN: Observational descriptive study. SETTING: Outpatient clinics. PATIENT(S): Nineteen males with hypogonadotropic hypogonadism, aged 14.5 to 31.0 years. INTERVENTION(S): Treatment with either hCG treatment alone (n = 9; group 1) or in combination with recombinant FSH (n = 10; group 2), over 6 to 9 months. MAIN OUTCOME MEASURE(S): Combined testicular volume (CTV) and testosterone, inhibin B, semen/urine analysis at 6 to 9 months. RESULT(S): There were no differences between the two groups in baseline variables or changes in CTV with treatment. Despite this, evidence of spermatogenesis was present in all group 2 patients by 9 months (range 0.2 to 15 × 10⁶/mL) compared with three of nine patients in group 1 (range 0 to <1 × 10⁶/mL). Whole group and subgroup analyses did not demonstrate any statistically significant correlations between age at onset of treatment and either CTV or sperm count. CONCLUSION(S): The addition of recombinant FSH to hCG treatment protocols in adolescent/young adult HH males results in normal testicular growth and may hasten induction of spermatogenesis.