The etiology of annular constrictions and/or intrauterine amputations is believed to be the result of an embryologic developmental defect or of a happenstance mechanical constriction. Evidence drawn from 3 infants and 1 fetus is used to evaluate the above theories. It is concluded that simple mechanical constriction is most likely not the etiology, and that a focal degenerative process is operative, which is consistent with the changes originally described by Streeter. In view of present embryologic concepts, this lesion is not a primary embryologic defect as postulated by Streeter, but a secondary superimposed disease process of unknown etiology.