Background Rupture of the costal margin is uncommon. Whilst most often seen after major trauma, we describe its occurrence in patients with no direct chest trauma. Methods A search was performed in our thoracic surgery database for all patients with rupture of the costal margin. Patients were excluded if the injury was a result of trauma. Data were collected on sex, age, body mass index, profession, past medical history, smoking status, presenting complaint, mechanism of injury, and management. Results There were 9 patients with rupture of the costal margin that was caused in all cases by a severe coughing fit. All patients were male and the mean age was 62.5 years (range 47–76 years). Chronic obstructive pulmonary disease was present in 6 cases. Presentations included a palpable defect (5 cases), cough (9 cases), and chest pain (6 cases). On radiological examination, all patients had widening of the rib space, 4 had associated rib fractures, and 5 had lung herniation. Time from injury to presentation was 12 months (range 1–24 months). All patients underwent surgery and were followed-up for 59 months (range 8–129 months). Two patients suffered major complications in the immediate postoperative period. Conclusions Rupture of the costal margin, in the absence of direct trauma, is characterized by pain, a palpable defect, and lung herniation. It is associated with widening of the rib space and rib fractures, and can be treated surgically with success but not without significant risks.