Penetrating trauma to the intrathoracic abdomen is a difficult clinical problem, especially with reference to the detection of diaphragmatic injuries. A retrospective analysis of 657 laparotomies for penetrating abdominal trauma at our institution revealed 78 laparotomies with negative results. The majority (44.8%) were for wounds in the lower chest and upper abdomen. The role of laparoscopy in evaluating these difficult areas was studied in 40 (34 stab wounds and 6 gunshot injuries) patients. Fifteen stab wounds and five gunshot wounds were nonpenetrating. Laparoscopy revealed eight clinically unsuspected diaphragmatic lacerations in seven patients. Twenty patients had hemoperitoneum. Five patients with omental bleeding and abdominal wall bleeding and four with nonbleeding liver lacerations underwent nontherapeutic laparotomies. One patient with a nonbleeding liver laceration was observed successfully without laparotomy. Ten of the 20 patients with hemoperitoneum had therapeutic laparotomies. The incidence of diaphragmatic lesions discovered by laparoscopy in this series was comparable with that reported after a mandatory laparotomy for thoracoabdominal wounds. It is concluded that laparoscopy is an excellent modality for the evaluation of the intrathoracic abdomen and the diaphragm.