Does a man’s ability to father children decrease with age? Interest in this question is increasing because of longer life expectancy, later age of parenting, and possibly declining sperm counts due to environmental factors. This seemingly simple question, however, does not have a simple answer.

In recent years, the media have profiled several high-wattage celebrities in their late 30s and early 40s who are having children. The trend toward delayed marriage and parenting does not appear limited to Hollywood. Data from the 2000 census and the most recent National Survey of Family Growth (NSFG) reflect this pattern as well.

EVEN THOUGH the American Urological Association has developed guidelines for numerous conditions, there are none for vasectomy. Yet this is one of the most common procedures performed by urologists, with more than 500,000 done annually in the United States.