With 12 FiguresAlthough aneurysms of the bifurcation of the internal carotid artery have been mentioned in passing in numerous papers describing personM experiences with intracranial aneurysms, reports devoted specifically to the problems created by such aneurysms are rare. Because we know of only two publications giving detailed descriptions of the carotid bifurcation aneurysms (TSnnis and Walter, 1966;David and Sachs, 1967) we thought it useful to describe our own experience with this aneurysmal pathology.Our series comprises thirteen patients. The essential clinical data of these cases are summarized in Table 1.These 13 patients (8 men and 5 women) represent 9.1% of all the intracranial aneurysms of our series. This percentage is higher than that of most other authors (4.4% Lol~sley, 1966; 6~o Crompton, 1962; 5% David and Sachs, 1967; 8% Frugoni and Ruberti, 1957; 9% Maspes and Marini, 1965). ~n 8 patients the aneurysm was on the right carotid bifurcation, in 5 on the left one. In two instances the internal carotid bifurcation aneurysm was associated ~dth a second intracranial aneurysm (anterior communicating artery: case XI; contralatera] internal carotid artery: case XII).The age of the patients ranged from 24 to 65 years; the average age was about 44 years and the highest incidence was between 40 and 50 years.A similar age distribution is found in the cases of David and Sachs (1967), whilst in the cases reported by Lo]csley (1966) the highest incidence occurred between 60 and 70 years.Six of our 13 patients had repeated bleeding (eases II, V, VI, X, XI and XII); however, on account of the presence of a second aneurysm, the origin of the bleeding in the cases XI and XII is open to doubt. Recurrent bleeding, so frequently observed in our cases, was also reported by Wright and Sweet (1963), although it does not appear to have occurred in David and Sachs 's experience (1967).In all patients--except case II[ in whom the clinical picture was independent of the carotid bifurcation aneurysm--the clinical picture 4*