OBJECTIVE We clarify the impact of removal of the tumor bearing testis on semen quality and reproductive hormones in men with testicular cancer. METHODS Semen quality and levels of reproductive hormones were investigated in 48 men before and after orchiectomy for testicular cancer. Semen analysis was done in 35 of these men and hormone analyses were done in 47. The hormone data of patients with (14) or without (33) elevated values of human chorionic gonadotropin (HCG) were analyzed separately. RESULTS Median sperm concentration and total sperm count decreased from 17 x 10(6)/ml. (range 0 to 117) and 39 x 10(6) (0 to 433), respectively, before to 7 x 10(6)/ml. (0 to 69) and 30 x 10(6) (0 to 200), respectively, after orchiectomy. After orchiectomy sperm concentration was decreased in 30 of 35 men (p = 0.001) and azoospermia developed in 3 (9%). In men without detectable HCG median follicle-stimulating hormone levels increased (p <0.001) from 5.7 IU/l. (range 0.01 to 30) before to 10.0 IU/l. (4.6 to 48) after orchiectomy in 33 of 33 patients. Median inhibin B significantly decreased (p = 0.003) from 108 pg./l. (range 60 to 193) before to 95 pg./l. (less than 20 to 141) after orchiectomy. Median luteinizing hormone increased significantly from 3.1 IU/l. (range 1.1 to 9.9) before to 5.2 IU/l. (2.1 to 27) after treatment (p <0.001). Testosterone and sex hormone-binding globulin did not change significantly after orchiectomy. Patients with detectable serum HCG before orchiectomy had a considerable increase in follicle-stimulating hormone after orchiectomy, and a concomitant decrease in testosterone and estradiol. CONCLUSIONS Semen quality was poor at diagnosis and deteriorated further after orchiectomy compared with pretreatment values. Our findings indicate that in some patients the most appropriate time for cryopreservation of semen is before orchiectomy. Androgen production was maintained by increased luteinizing hormone stimulation after orchiectomy.