Hereditary multiple exostoses, also known as diaphyseal aclasis or osteochondromatosis is an autosomal dominant condition, characterized by the development of multiple osteochondromas.Hereditary multiple exostoses demonstrate an autosomal dominant inheritance pattern, with incomplete penetrance in females. The number of exostoses, the degree, and type of angular deformity, and even the rate of malignant transformation varies significantly, even within families.Most patients are diagnosed by the age of 5 years, and virtually all are diagnosed by the age of 12 years. Patients may be asymptomatic with a few small lesions or may be significantly deformed by multiple large osteochondromas. Except that they are multiple, imaging features are identical to solitary osteochondromas. The skeletal distribution of lesions can significantly vary, with some authors noting that the typical distribution is bilateral and symmetric, whereas others report a strong unilateral predominance.Often associated with a broadened shaft at the end of long bones, hence the term diaphyseal aclasis.