To assess the need for therapeutic laparotomy in patients with blunt abdominal trauma (BAT), ultrasonography (US) and a simple US scoring system were used to estimate the amount of hemoperitoneum during resuscitation. In group I (BAT with a US score > 3), 24 of 25 patients (96%) required therapeutic laparotomy. In group II (BAT with a US score < 3), therapeutic laparotomy was required in only 9 of 24 patients (38%); nonsurgical treatment may be justified in hemodynamically stable patients. Appropriate decisions can be made to perform urgent laparotomy when intra-abdominal bleeding is the culprit in BAT patients. Unnecessary laparotomy can be avoided when the major site of blood loss is not in the abdomen. Ultrasonography, an initial rapid screening procedure in BAT patients, is useful for trauma surgeons in decision making during resuscitation.