The incidence of burst abdomen, incisional herniation, and sinus formation after a vertical abdominal incision was studied in a prospective randomized trial that compared two suture materials--monofilament nylon and polyglycolic acid. Laparotomy wounds were closed with a continuous mass suture technique. Of the 210 patients studied, 15 died between 10 days and 6 months postoperatively with their wounds intact. The remaining patients were followed up for 6 months or longer. The two groups were well matched for known risk factors. The 104 patients in the polyglycolic acid group had a 12.5% wound failure rate (1 burst abdomen and 12 hernias), but the 106 patients in the nylon group had only a 4.7% wound failure rate (1 burst abdomen and 4 hernias) (P = 0.04). There was a significant association between the rate of infection and sinus formation, but there was no difference between the incidence of these complications between the two groups. Closure of abdominal wounds with absorbable sutures does not appear to be justified, and we suggest that nylon and the mass closure technique be used for all abdominal wound closures. Other etiologic factors significantly associated with wound failure include male sex and postoperative chest complications. However, infection remains the most significant postoperative complication because the incidence of incisional hernias and sinus formation would be reduced by the elimination of wound sepsis.