In diaphyseal aclasis, the exostoses usually involve long bones, although occasionally the spine is also affected. Very few cases of osteochondroma causing spinal cord compression have been cited. The authors report their experience with two cases of diaphyseal aclasis. In the first case spinal cord compression caused by an exostosis of the lamina of C-2 occurred in a 9-year-old boy; in the second case a large osteochondroma of C-5 occurred in a 45- year-old man. Also included in this report is a review of the literature highlighting the incidence of diaphyseal aclasis, its clinical features and its excellent prognosis in treated cases.