Factors determining the rate of disappearance of sperm from the ejaculate after vasectomy.

The relative importance of age and frequency of coitus in determining the time needed for the semen count to become negative after vasectomy was studied in a group of 831 men. Irrespective of the frequency of coitus, there was a highly significant positive correlation between a patient's age and the time taken to become aspermic. This has implications for general practice: the older patient should be warned that he will take longer than a younger man to become sterile.