Intra-abdominal heterotopic ossification is extremely rare with only approximately 30 cases having been reported. While most reported cases have involved the mesentery, ossification of the peritoneum is even rarer. The pathogenesis remains undetermined but is generally considered a reactive process in response to various stimuli. Histologically, it is composed of a peripheral area with bone formation and a central area of reactive hypercellular fibrous tissue. We report a rare case of intra-abdominal heterotopic ossification of the parietal peritoneum following traumatic splenic rupture.