Background: The incidence of diaphragmatic hernias caused or exacerbated by diagnostic colonoscopy is not well elucidated at this time, and is believed to be very rare. Case Presentation: We present the case of a 57 year old man with remote history of traumatic injury who first presented with vague left shoulder pain for two weeks, mild anemia, and tested positive for fecal occult blood. Four days post colonoscopy the patient was found to have a strangulated loop of bowel herniated through the diaphragm into the left hemithorax. Conclusions: In patients with previous history of serious traumatic injury and particularly those with previous splenectomy, a thorough history and physical examination before routine colonoscopy is important. A high level of suspicion for post-operative complications should also be maintained when assessing such patients.