Varicocele was surgically induced in monkeys to study the long-term effects of the condition on seminal and testicular parameters. Sperm motility was depressed but improved after varicocelectomy. Sperm concentration was less affected, but sperm morphology showed long-term degenerative changes, i.e., for more than 2 years. Testicular blood flow was depressed acutely but returned to normal after 2 years. Electron microscopy showed changes in the basal lamina and spermatogonia that persisted throughout the study. Left adrenalectomy, at the time of varicocele induction, did not alter the development of varicocele-related changes. The sequence of changes suggests that the effects of this experimental varicocele may be reversed in the monkey model through changes in collateral and ancillary revascularization.