A new type of mesomelic dwarfism in two male siblings and their father is presented. The responsible mutant gene manifests itself phenotypically as a severe dysostosis of the tibia with shortening, bowing and pseudarthrosis and as a mild dysostosis of the radius. The fibulae and ulnae are secondarily affected, but the rest of the skeleton is normal. The disorder has an autosomal dominant mode of inheritance. It can be differentiated rather easily from the already known forms of mesomelic dwarfism.