BACKGROUND Despite the predominance of superficial injuries after explosive blast exposure, major morbidity or mortality among immediate survivors is caused by delayed perforation of intestinal mural contusions. Previous studies have suggested that small bowel and colonic contusions larger than 10 mm in diameter are at high risk. This experimental study aimed to identify contusions at high risk of late perforation. METHODS Histological features of injury were classified in 188 blast-induced intestinal contusions in 16 anaesthetized Large White pigs. RESULTS Some 16 per cent of small bowel and 12 per cent of colonic contusions were at high risk of late perforation. Small bowel contusions larger than 15 mm in diameter had a worse histological grading than those smaller than 15 mm (chi 2 = 0.09, 2 d.f., P = 0.01). Contusions that extended over more than half the bowel circumference (chi 2 = 14.79, 2 d.f., P = 0.0006) and those affecting the mesenteric border (chi 2 = 7.5, 2 d.f., P = 0.024) were more severe injuries. Colonic contusions larger than 20 mm in diameter had a worse histological grading than smaller ones (chi 2 = 14.95, 2 d.f., P = 0.0006). Confluent, rather than diffuse, colonic contusions were more severe injuries (chi 2 = 6.37, 2 d.f., P = 0.04). CONCLUSION Once identified at laparotomy, the number of small bowel contusions requiring excision may be reduced from 86 to 60 per cent; similarly, excision of colonic contusions can be reduced from 73 to 27 per cent if small bowel contusions smaller than 15 mm in diameter and colonic contusions of less than 20 mm are managed conservatively.