AIM: Presentation and discussion of a case of heterotopic ossification of a vertical abdominal surgical scar. PERSONAL OBSERVATION: A recent trauma in an 70 year old patient, followed by a sudden internal hemorrhage because of a penetration in abdomen of a bone stump, originated from a fracture of a not known heterotopic ossification of an old median abdominal scar, of a laparotomy of many years earlier for perforated duodenal ulcer. RESULTS: An emergency surgery was mandatory DISCUSSION: Pathogenesis of heterotopic ossification, as rare metaplastic phenomenon outside of the normal bone tissue, still unknown and speculative. CONCLUSION: Despite the rarity the complications of heterotopic bone formation can also be very dramatic following a trauma that transforms the new bone into traumatic agent, as in the present observation.