Objectives. To determine the frequency of secondary azoospermia after microsurgical vasovasostomy and to determine what factors increase the risk of its occurrence. Methods. We performed a retrospective review of three surgeons' experience. Patency was defined as the presence of sperm in at least one postoperative semen sample. Transient patency was defined as azoospermia or no motile sperm after previous documentation of motile sperm. Results. A total of 242 patients underwent 245 procedures (233 bilateral, 12 unilateral). The mean patient age was 39.2 ± 0.4 years (range 24 to 56), and the mean obstructive interval was 8.7 ± 0.3 years (range 0.25 to 24). The patency rates were 91% (224 of 245, sperm present in the semen) and 86% (208 of 245, motile sperm present in the semen). The transient patency rates were 5.3% (13 of 245, presence of sperm, with subsequent azoospermia) and 2.9% (7 of 241, motile sperm in the semen, with subsequent azoospermia) at a follow-up of 9.0 ± 0.7 months (range 1 to 60). Transient patency occurred at a mean of 9.7 ± 2.3 months. A greater risk of transient patency was observed with unilateral cases than bilateral cases (3 of 12, 25% versus 10 of 233, 4.3%; P = 0.0196, Fisher's exact test), and the obstructive interval was shorter for patent than for transient patent cases (Mann-Whitney U test, P = 0.0458). Conclusions. The results of our study demonstrated that secondary azoospermia after vasovasostomy is rare. It is more common in unilateral cases and the obstructive interval for transiently patent cases is longer. Sperm cryopreservation, when motile sperm appear in the semen postoperatively, can circumvent the problem of secondary azoospermia, but most men will not need the frozen sperm. © 2005 Elsevier Inc.