A series of 53 patients with multiple injuries and suspected abdominal trauma were analysed to determine the accuracy of diagnostic laparocentesis and peritoneal lavage. Thirty-one positive findings resulted in immediate laparotomies. Fifteen patients with an otherwise strong suspicion of intra-abdominal injury were treated conservatively with an uneventful clinical course. All three false-negative findings were in patients who has previously been subjected to laparotomy. These 3 patients were laparotomized on the basis of other diagnostic evidence. Four positive and two false-positive findings resulted in unnecessary operations. Trocar laparocentesis combined with peritoneal lavage is a quick and safe aid in the diagnosis of blunt abdominal trauma. Trauma to the urinary tract, however, should be diagnosed without laparocentesis. The test does not replace other diagnostic methods, but it may shorten the preoperative delay in complicated situations.