Diagnostic peritoneal lavage (DPL) is a valuable triage tool in the evaluation of patients with abdominal trauma. Observation after a negative lavage is necessary to detect injuries not well discerned by DPL performed in the early postinjury period. We evaluated the use of 12 hours of monitoring in an emergency department observation unit in the management of 230 patients with abdominal trauma and a negative initial DPL. One hundred five of the patients had blunt and 125 had penetrating trauma. One hundred eighty-seven patients (81%) were discharged home from the observation unit without any reported significant complications. Thirty-eight patients (17%) required admission to our hospital; four of the 38 underwent necessary laparotomy. In the 230 patients evaluated, no deaths or complications could be assigned to the use of 12 hours of observation in the unit. The use of an observation unit in our study resulted in the potential savings of $51,329. Our study supports the concept that selected patients with significant abdominal trauma and a negative DPL can be managed safely and cost effectively in an ED observation unit.