A 48 years old man presented with subacute intestinal obstruction resulting from an intraluminal colorectal mass. He underwent partial colectomy. Histological diagnosis of mucinous adenocarcinoma with focal areas of heterotopic ossification was made. Although the presence of heterotopic ossification has no known prognostic implication in colorectal carcinoma, however, it is important that both radiologist and pathologist be aware of this phenomenon as distinct from carcinosarcoma that has poorer prognosis. From the available literature reviewed and to the best of our knowledge, this is the first reported case of mucinous colorectal carcinoma with heterotopic ossification in Saudi Arabia.