Individuals with deletions of the proximal portion of the short arm of chromosome 11 share many manifestations including mental retardation, biparietal foramina, minor facial anomalies, and multiple cartilaginous exostoses. The finding of multiple exostoses in these patients is remarkable as the disorder hereditary multiple exostoses, which is inherited in an autosomal dominant manner, has recently been mapped by linkage to three regions, including proximal 11p. We report the clinical and molecular findings in an additional patient with an 11(p11.2p12) deletion. Cytogenetic and molecular analysis demonstrated a de novo, paternally derived deletion for markers which have been shown to be tightly linked to the 11p locus (EXT2). These data support the location of EXT2 within this region and also provide information regarding the ordering of polymorphic markers on 11p. Deletion 11(p11.2p12) is a rare, yet specific, deletion syndrome involving the EXT2 locus, a gene for parietal foramina, and a mental retardation locus, and therefore can be classified as a contiguous gene deletion syndrome.