In the belief that ordinary methods of research into pathologic conditions in twins are incorrect and do not furnish reliable data, the author, accompanied by his wife, spent three years touring the Reich, exclusive of East Prussia, in an attempt to study the occurrence of clubfeet in twins. The completeness of the work was aided by the fact that for the last ten years in Germany every instance of congenital anomaly has been reported to the social service. There was, therefore, a total of 11,459 instances of clubfeet, of which official information was obtainable about 9,941 (86.8 per cent). One thousand five hundred and eighteen clubfooted persons (13.2 per cent) could not be traced. From twin births there were recorded instances in 304 persons, of whom 290, or 95.4 per cent, were examined, but data about only 242, or 83.4 per cent, were used in the compilation of this paper.