Two Puerto Rican infants, offsprings of nonconsanguineous parents, died with spondylothoracic dysostosis as characterized by widespread anomalies of the spine (malformed vertebral bodies including hemivertebrae), deformity of the thorax, and fan-like configuration of the ribs. The disease was lethal in early life in the 18 cases previously reported. An autosomal-recessive inheritance has been described. Spondylocostal dysostosis, a related entity, showed associated intrinsic anomalies of the ribs. The 17 cases culled from the literature pursued a milder course, affected mainly older children and adults, and had a different pattern of inheritance.