Abstract Failures after abdominal wound closure (early dehiscences and late incisional hernias) are due to breakage of sutures, slippage of knots or tearing out of sutures from the tissues. The suture-holding capacity of the entire thickness of muscle and aponeurosis is nearly twice that of the anterior rectus sheath, and deep bites (1·0 cm from the cut edges) are nearly twice as secure as bites of 0·5 cm. In a random controlled clinical trial of 357 major laparotomies, closure with either layered monofilament nylon or mass polyglycolic acid or steel resulted in 2 burst abdomens (0·56 per cent), 10 incisional hernias due to suture failure (3·4 per cent) and 8 incisional hernias caused by deep sepsis (2·7 per cent). There were no statistically significant differences among the treatment groups, but 1 patient in the nylon and 3 in the steel groups had persistent sinuses until their sutures were removed.