In a survey of individuals with dwarfism in which 148 cases of typical achondroplasia were diagnosed, an additional group of 13 individuals was found to have an allied condition that was clearly a distinct entity. This is hypochondroplasia, a chondrodystrophy with roentgenographic changes similar to but milder than those of achondroplasia and without involvement of the skull. Hypochondroplasia is a heritable condition with autosomal dominant transmission. The diagnosis can only be established by roentgenographic examination.