Seventeen patients thought to have lethal osteochondrodysplasias were evaluated. Diagnosis was established through clinical evaluation, radiological studies and necropsy. Genetic counseling was provided to the affected patient's families. Specific diagnosis was confirmed in 16 cases. Nosologic diagnosis was done through clinical evaluation. However, the most efficient method for verifying the diagnosis was a skeletal radiological study. This fact corroborates the orientation of the International Classification of Osteochondrodysplasias (International Working Group on Constitutional Disease of Bone, 1992) in which a radiological criterion was adopted as the most relevant for classification of osteochondrodysplasias. An anatomopathological study was also done to detect internal anomalies, and was effective in identifying abnormalities in epiphyseal growth plate in a bone fragment study. This method had low specificity, but in two cases it was especially decisive for diagnostic differentiation.