General and anomalous sperm disappearance characteristics found in a large vasectomy series.

There is no accepted standard for the time after vasectomy before infertility is achieved. To help address this question, the records of 5,233 vasectomy patients who had had at least 12 ejaculations and had completed semen tests were reviewed. Seventy-five percent were able to fulfill a designated criterion for success by 4 months postoperatively, nearly 90% by 6 months, and nearly 99% by 1 year. Also found were a number of individual anomalies, including five instances of transient reappearance of sperm, four late spontaneous reversals after proof of success, and one late "delayed success" after evidence of failure. Patients can be reassured by the overall efficacy of male sterilization, but physicians also may wish to be aware of the possibility of capriciously intermittent-fitful-sperm.