The number of thrombi, ball or pedunculated, of the left auricle reported has been small, and Abramson1states that thrombi which form before death are a relatively uncommon postmortem finding. Welch2in 1899 collected twenty-five instances of "pedunculated polyps" in the left auricle. Covey, Crook and Rogers3found twenty-one cases of ball thrombi reported in the literature up to 1928 and added two of their own. Scott and Saphir4reported a pedunculated thrombus in 1928 and Schwartz and Biloon5added three cases in 1931. In all these cases, auricular fibrillation and mitral stenosis were present except in one of hypertension of Schwartz and Biloon. Von Ziemssen6was the first to conclude that mitral stenosis was necessary for the formation of auricular thrombi, but this was disproved by the case of Schwartz and Biloon and now by ours, in which there was an unusually large mitral valve. The authors