The heterotopic bone formation may occur in vertical upper abdominal midline scars. Fifteen such patients are reported. They all had annoying pressure symptoms and seven of them were operated due to the symptoms. The excised bone formation was located between the fascia and peritoneum fixed to the fascia. The ossification of the upper midline abdominal scar seems to be ten times more common in men than in women. The bone formation of the scar may cause problems in differential diagnosis, especially in the early phase of calcification. The radiological diagnosis is usually easy, either by plain roentgenography or if oblique views of the abdomen are taken.