From the literature, one gathers the impression that transposition of the viscera is an exceedingly rare condition. However, the fact that twenty-nine cases have come under my personal observation would make it appear that the condition is not as infrequent as it has been considered in the past. This is accounted for by the fact that the number of individuals studied by the roentgen ray is vastly in excess of those studied post mortem in the anatomic or pathologic laboratories or observed in the operating room. Former statistics were based on the latter observations, while present statistics are made from roentgen-ray observations. During the World War, when large groups of soldiers were examined roentgenographically, one observer is said to have found the frequency of transposition of the viscera to be one in 3,000 in a certain group examined. The experience of this medical officer was unique and probably overestimates the