Intraabdominal heterotopic ossification is a very uncommon disorder. We report five new cases, review the previous literature, and discuss the clinical and pathologic features of these lesions. The clinical features of the current cases and of those previously reported are remarkably similar. All patients were middle-aged to elderly men (range, 43-80 years; mean, 61 years) who had small bowel obstruction associated with heterotopic bone formation in the small bowel mesentery, often after one or more abdominal operations. In one case, an initial diagnosis of extraosseous osteosarcoma was considered. This unusual reactive process shares many of the clinical and pathologic features of myositis ossificans, as classically described in somatic soft tissues. We propose to designate this condition heterotopic mesenteric ossification.