To identify the mutation in the disease gene and provide prenatal diagnosis for a hereditary multiple osteochondromas (HMO) family.The exons of EXT1 gene in the proband with HMO and his family members were amplified by PCR. The products were analyzed by direct sequencing. Prenatal genetic diagnosis was performed by amniocentesis sampling after genotyping the proband.In the family, the affected proband was heterozygous of the mutation of 1476_1477delTC in the EXT1 gene, and the proband's father carried the same mutation in part of his somatic cells. No mutation was found in the EXT1 gene of the proband's mother and other 11 siblings of his father.METHODS for molecular diagnosis and prenatal diagnosis of HMO were established and applied to a family of HMO.