OBJECTIVE: To demonstrate the efficacy and safety of follitropin alfa administered with hCG on spermatogenesis in adult male hypogonadotropic hypogonadism (HH) patients. DESIGN: Phase III, multicenter, open-label, noncomparative. SETTING: Seven US medical centers. PATIENT(S): A total of 36 adult males with severe HH. INTERVENTION(S): A total of 1,000 U hCG on alternate days for 3 to 6 months, with dose adjustments after 2 months, if necessary, to normalize T levels, followed by follitropin alfa 150 U and hCG on the same alternate days for 18 months, with dose adjustments as necessary. MAIN OUTCOME MEASURE(S): Proportion of patients with sperm density > or =1.5 x 10(6)/mL. Pubertal advancement and long-term safety and tolerability were also evaluated. RESULT(S): In total, 22 of 29 patients (75.9%) who received > or =1 dose of follitropin alfa and 20 of 25 patients (80%) who completed 18 months of hCG + follitropin alfa treatments achieved a sperm concentration > or =1.5 x 10(6)/mL. A sperm concentration >20 x 10(6)/mL was achieved by 8 of 29 men (27.5%). Median sperm concentration at 18 months was 5.2 x 10(6)/mL. Pubertal development continued during the study, and testis volumes increased. Five clinical pregnancies were achieved. Acne (52% of patients) was the most common side effect, and gynecomastia was reported in 10% of patients. CONCLUSION(S): Long-term treatment of azoospermic HH men using follitropin alfa and hCG is effective for stimulating spermatogenesis and is well-tolerated.