The long-term outcome of cryptorchism (undescended testis) was studied in 43 patients who underwent orchidopexy at pre-puberty ages and who were over 15 years of age at the time of this study. The follow-up period after operation was 11 approximately 23 years. Cryptorchism was unilateral in 39 patients and bilateral in 4 patients. The sperm concentration and motility were examined, using a cut-off level of 20 x 10(6)/ml for sperm concentration and 50% for sperm motility. In the unilateral cryptorchism group, 16 patients (61.5%) had normal semen quality, 8 patients (30.8%) oligozoospermia, 1 (3.8%) asthenozoospermia and 1 (3.8%) azoospermia. In the bilateral cryptorchism group, 3 patients (75.0%) were normal and 1 (25.0%) had azoospermia. Eight patients with unilateral cryptorchism were married and 7 of them (87.5%) had children. The sperm concentration had no inverse correlation with the age at operation. In patients with unilateral cryptorchism, the testicular volume on the healthy side was significantly higher than that on the affected side. The sperm concentration tended to correlate with the testicular volume on the healthy side rather than that on the affected side. These findings suggest that the sperm profiles in patients with unilateral cryptorchism are chiefly associated with the testicular function on the healthy side.