Onset of azoospermia after vasectomy.

Nine hundred and sixteen men who had undergone bilateral vasectomy were followed up with semen analysis at monthly intervals. After an average of 10 ejaculations at least 35% of men still had non-motile sperms at the end of the first month. This persisted in four men even after 50 ejaculations or more. The reasons for, and the implication of the very slow clearance of spermatozoa after vasectomy are discussed.