Thanatophoric dwarfism and achondrogenesis are lethal forms of skeletal dysplasia with clinical, radiographic, and genetic features distinct from classic achondroplasia. Both of these forms of lethal chondrodystrophy continue to be mistaken for achondroplasia, with serious genetic implications, since present evidence suggests that at least achondrogenesis is the result of autosomal recessive inheritance. This report presents the clinical, radiographic, and autopsy findings in three short-limbed infants who died soon after birth. Early death is due to respiratory insufficiency secondary to severe pulmonary hypoplasia and, in one case, dysplasia of the tracheal rings. The incidence of lethal chondrodystrophies is about one in 19,000 live births. It is suggested that the differential diagnosis between thanatophoric dwarfism and achondrogenesis can be established unequivocally on radiographic grounds, as can the differentiation of these two lethal skeletal dysplasias from classic achondroplasia. It is important for proper genetic counseling that these distinctions be made.