Intercostal hernias with abdominal viscera have rarely been reported following penetrating accidental or surgical trauma. We report herein a case of a traumatic rupture of the left hemidiaphragm, presenting as an intercostal hernia 2 years after a penetrating thoracoabdominal injury. The diaphragmatic rupture had been initially very small and could not be detected in the serial chest films and abdominal computed tomographic scans. The injury was also missed during an exploratory lateral thoracotomy. The patient was admitted with the chief complaint of a painful and gradually enlarging left-sided chest wall bulge of 8 months' duration. Surgery via an anterolateral thoracotomy along the axis of the intercostal hernia was performed, and the omentum and splenic flexura of the colon were reduced.