The accuracy of initial physical examination and peritoneal lavage in detecting intra-abdominal injury was assessed in 221 consecutive blunt trauma victims. Of the patients, 121 had negative peritoneal lavages, with one false result, and 100 had positive peritoneal lavages, including six false results and two injuries not requiring surgical correction. Hemoperitoneum occurred in 32 of 71 patients with a depressed sensorium and in 29 of 54 patients with thoracic injury. Twenty-eight of 120 patients with absent bowel tones and 20 of 100 patients with abdominal guarding or rigidity had negative peritoneal lavages. Among the 150 conscious, responsive patients there was a high incidence of false-positive and false-negative abdominal findings on physical examination. Hemoperitoneum was detected in four clinically negative patients. Significant error accompanies the initial abdominal examination and clinical assessment in the blunt trauma victim. In contract, open diagnostic peritoneal lavage is a sensitive and highly accurate test for blunt intraperitoneal injury. We believe peritoneal lavage is the single best test for intra-abdominal injury and should be performed in th majority of patients with such injuries.