The evaluation of penetrating thoracoabdominal trauma for the presence of a diaphragmatic injury presents a diagnostic challenge to the trauma surgeon. The use of diagnostic laparoscopy (DL) in this setting was reviewed at a level-one trauma institution. Eighty patients (71 males, 9 females) with penetrating injuries to the thoracoabdominal region underwent DL to rule out injury to the diaphragm. Fifty-eight patients (72.5%) had a negative study and were spared a celiotomy. In the remaining 22 patients (27.5%), injury to the diaphragm was identified. This subset of patients underwent a mandatory celiotomy to rule out an associated intra-abdominal injury. Seventeen out of 22 (77.2%) patients had a positive exploration requiring surgical intervention, representing an associated intra-abdominal injury rate of 21.2 per cent. Intra-abdominal injuries requiring repair included small bowel, colon, spleen, liver, and stomach, in descending order. There were no missed injuries or deaths. One patient with a left diaphragmatic injury secondary to a stab wound developed a subdiaphragmatic abscess. Respiratory insufficiency secondary to atelectasis was the most common complication. Diagnostic laparoscopy is an essential and safe modality for the evaluation of diaphragmatic injuries in penetrating thoracoabdominal trauma.