The aim of the study was to compare the effects of human chorionic gonadotropin (hCG) therapy with those of surgical or combined therapy on testicular volume (TV) in boys at different ages with unilateral canalicular undescended testis (UDT). In total, 155 boys aged 1 to 12 years were treated: either surgically (ST), or by 50 IU/kg body weight hCG administration every three days for five weeks (HT), or by a combination of the two. The patients underwent ultrasound examination of TV before the treatment, 9-12 (median 10) and 24-39 months (median 32) after therapy. The testicular atrophy index (TAI) of the affected testicle was calculated. The success rate was 94.7% for ST, 39.2% for HT and 98% for HST patients. The atrophy rate was 5.3% for ST, 0% for HT and 2% for HST. Neither treatment type nor patient age significantly influenced gonadal atrophy. No significant differences in TV of the affected testis were observed after treatment between the groups. The TAI values were significantly the lowest in HT group (p = 0.0006). Both TV and TAI changes from the baseline values did not differ between the treatment groups. At the 24- to 39-month follow-up, no significant differences were observed in the change in baseline TV and baseline TAI between age groups. TV of the affected testis increased significantly (p = 0.0000), and TAI decreased significantly over time (p = 0.01), with no significant differences depending on the age group, treatment type or the interaction of the two factors. The hCG therapy did not impair the development of affected and healthy testes, neither as single nor as neoadjuvant therapy, both during early assessment and after 2-3 years. Patients' age at the initiation of treatment seems irrelevant.