The type II collagenopathies represent a group of chondrodysplasias sharing clinical and radiological manifestations which are expressed as a continuous spectrum of phenotypes, ranging from perinatally lethal to very mild conditions. Their common molecular bases are mutations in the type II collagen gene (COL2A1). We describe one case of lethal platyspondylic dysplasia, Torrance type, and a variant of lethal Kniest dysplasia, neither of which has been reported as a type II collagenopathy. Biochemical studies of cartilage collagens and morphological analysis of cartilage sections suggest that abnormalities of type II collagen structure and biosynthesis are the main pathogenetic factors in both cases. Thus, the phenotypic spectrum of type II collagenopathies might be greater than hitherto suspected.