Six cases of a new hereditary chondrodyplasia are reported. The features are severe dwarfism, generalized hypotonia, frequent and considerable desaxations of fingers and toes. Slight facial dysmorphism with evolutive scoliosis is often associated. Osteopetrosis is diffuse and is associated with important metaphyseal widening as well as epiphyseal irregularities and often carpal and tarsal supernumerary bones. No metabolic or chromosomal abnormality was found. The relations of the disease with related types described in Larsen's syndrome are considered.