Genetically different bone dysplasias may manifest themselves in similar patterns of skeletal abnormalities. It is proposed to group these similar dysplasias in 'families' for two reasons: 1 The knowledge of developmental patterns shared by different genetic disorders cautions the diagnostician and encourages a two-step procedure: a) provisional recognition of a pattern and b) more careful analysis of the pattern to reach a final, specific diagnosis. 2 Families of bone dysplasias may be the result of similar pathogenetic mechanisms. Once the mechanism is discovered in one member of the family, a search for similar mechanisms in others may be rewarding. An example of such a pattern is dysostosis multiplex. It is found in a family of disorders caused by defects of complex carbohydrate degradation. The present study delineates four more patterns and their families: the achondroplasia pattern, spondyloepiphyseal dysplasia congenita pattern, the Larsen/OPD pattern and the Stickler/Kniest pattern.