Although a search through the literature does not seem to substantiate the fact that aneurysm in this situation is common, it undoubtedly impresses one that the lesion is sufficiently frequent for the clinician to keep in mind. FREQUENCY The frequency of this aneurysm is difficult to compute accurately. Among the "special features" pointed out by Osler1are the statements: "It is often latent, causing sudden death by rupture into the pericardium. It is a medicolegal aneurysm met with in coroners' cases." Possibly because of this a large percentage of cases do not get into the records. Cattell and Steele,2in reporting a case of aneurysm of the sinus of Valsalva, state that it is a very rare pathologic lesion, their case being the first in 2,000 necropsies. In 3,108 necropsies Bosdorff reports two. In the Middlesex Hospital Reports, containing protocols of 3,030 cases, there were two of aneurysm