Many patients undergoing laparotomy will have had a previous incision in the abdominal wall which offers a convenient and logical route for reexploration. This study aims to examine the risk of subsequent incisional herniation in incisions made through previous scar tissue compared with incisions made through fresh tissues. Out of a total of 1022 laparotomies performed in a 5-year period on one surgical unit, the incisional hernia rates were available for assessment in 699 freshly made incisions, 142 reincisions and 36 incisional hernias. The incidence of incisional hernia was 6 per cent after freshly made incisions and this incidence was increased after both re-incision (12 per cent, P less than 0.05) and incisional hernia repair (44 per cent, P less than 0.01). With the exception of jaundice, none of the other commonly accepted risk factors for incisional herniation were significantly increased in those patients with re-incised wounds who subsequently developed a hernia, when compared with patients who did not develop a hernia. An increased risk of incisional herniation is present when laparotomy is performed through a previous abdominal incision.