Congenital absence of part or all of the sacrum is of infrequent occurrence. Gross aplasia (frequently called agenesis) of the caudal portion of the spine from the mid-thoracic level or higher is probably incompatible with life at an early stage of fetal development and would therefore tend to be unreported. Absence of the terminal part of the coccyx would also be likely to remain undetected unless found during unrelated roentgen studies. An analysis of spinal roentgenograms of 700 children was made by Shands and Bundens (1) in 1956. In a group of 169 anomalies, there were 5 cases of absence of spinal segments, 3 of congenital absence of all or part of the lumbar spine, sacrum, and coccyx, and 1 of solitary coccygeal absence. In 1852, Hohl (2) reported absence of the sacrum for the first time. The first complete review of this subject, however, was presented by Freedman (3) in 1950. By that time, 54 cases had been reported, to which Freedman added a fifty-fifth. An excellent and comprehensive review by Bl...