The failure rate for vasectomies is around the same for tubal ligation: 1 in 2,000 vasectomies fail, as noted by the Male Health Center. Vasectomies are considered permanent birth control for men, and it prevents the release of sperm with the male ejaculate fluid, according to WebMD.
WebMD cautions that it can take several months after the procedure for residual sperm to be released or reabsorbed by the body. During this time, a vasectomy is not as reliable, since sperm present before the procedure may cause pregnancy. A semen sample test showing a sperm count of zero is needed before it is safe to have sex without using an alternate form of birth control.