We report two patients who developed a post-traumatic flank hernia manifested several months after road traffic accidents. The diagnosis was missed and established later when a swelling appeared in he flank. CT Scan found a large parietal defect. Treatment by implanting a mesh of non-absorbable material was successful. Post-traumatic flank hernias are rare. The diagnosis may be clinically difficult and is mainly based on CT scan examination. A delayed repair is recommended.