Treatment of anorectal abscess with or without primary fistulectomy. Results of a prospective randomized trial. To determine whether primary fistulectomy should be performed or not at the time of incision and drainage, a prospective, randomized study in 70 patients with anorectal abscess was conducted. Thirty-six patients underwent incision, drainage and fistulectomy with primary partial internal spincterectomy (group I), whereas in 34 patients anorectal abscess was treated by incision and drainage alone (group II). After a median follow-up of 42.5 months, the combined recurrence or persistence rate was 2.9 percent in group I and 40.6 percent in group II (P less than 0.0003, log-rank test). Recurrent abscesses or persistent fistulas were treated by secondary partial internal sphincterectomy. Comparing anal continence before and 1 year after definite treatment, we found increased anal function disturbances in 39.4 percent of the patients in group I and in 21.4 percent of the patients in group II (P less than 0.106, Fisher-exact test). The combined recurrence or persistence rate of 40.6 percent indicates that more than half of the patients with anorectal abscess will have no further problems after simple incision and drainage. This finding, as well as the increased anal function disturbances after partial internal sphincterectomy (either primary or secondary) are the main reasons to reserve fistulectomy as a second stage procedure if necessary. 