OBJECTIVES: Vasectomy is a surgicalmethod of male contraception. Azoospermia is offered as result of the technique and this is not always attained, resulting in legal matters. The purpose of this study is to know the number of semen samples needed to dischargea patient after intervention. To identify sperm count on semen analysis at time of discharge.METHODS: Retrospective study of men who underwent vasectomy in a 15-month period with a 2 year follow up. Consecutive semen analyses up to 5 samples were measured at 2 to 3 months interval in all men who had persistence of spermatozoa.RESULTS: 618 men were intervened, 106 did not bring semen to the laboratory (17 %), 2 (0.39%) presented motile sperm and were considered a failure of thetechnique and excluded. 510 men completed controls. 316 (61.9%) were azoospermic in the first sperm analysis,74 (14, 5%) in the second, 27 (5, 2%) in the third, 6 (1, 2%) in the fourth and one (0, 2%) in the fifth analysis. The remaining 86 men (16.8%) had persistence of immotile sperm in the ejaculate and were less than 100,000/ml. No pregnancy was reported during 2 years follow up or after.CONCLUSIONS: Five or more semen analysis can be made after the surgery. Persistence of immotile sperm in the ejaculate is frequent and may exist for a long period afterwards. Immotile sperm count of 100.000/ml or less should be accepted as result of the procedure. The patient should be informed about the fact that persistent immotile sperm can be found in his semen. In the informedconsent azoospermia should not be a concern as it is frequent to find immotile sperm in the ejaculate and this is an acceptable issue. As with other contraceptivemethods, vasectomy should be offered as a safe method although clearly stating that the possibilities of failure do exist.