Hematoma. This results from bleeding into the scrotum. It can get large and painful, and turn the scrotum black and blue. Incidence with conventional vasectomy is around 3%. The NSV literature puts it at 0.3% which is in line with my experience.
Infection. Minor infections occur in about 2% of patients. Serious infections, requiring intravenous antibiotics or drainage of an abscess occur in less than 0.1% of cases. Even the rare serious infections usually resolve completely in a few weeks.
Vasitis or Epididymitis. Inflammation and swelling of the tissue surrounding the vas or extending down around the epididymis (the part just below the vas that joins it to the testicle) occurs about 2% of the time. It’s usually mild and transient, no bigger than a grape. Sometimes it can be painful, but this too will settle with persistent use of anti-inflammatory drugs (NSAIDS such as ibuprofen).