Post-vasectomy semen analysis is used to confirm sterility after vasectomy. A review of 56 studies found that most patients showed azoospermia (no sperm) after 3 months and 20 ejaculations. Some patients had persistent nonmotile sperm, but eventually achieved azoospermia. Reappearance of nonmotile sperm was rare and occurred up to 22 months after vasectomy. The evidence suggests that one test after 3 months and 20 ejaculations is enough to confirm sterility, with periodic testing if needed. Patients with low levels of nonmotile sperm may still have successful outcomes. Histological testing of the vas deferens is not necessary based on the findings.