Objective ‒ to determine the main x-ray anatomical characteristics of arterial aneurisms (AA) of bifurcation of basilar artery (BA) and predictors of hemorrhagic transformation, taking into account the main options for the course of the disease.Materials and methods. Total on examination and treatment in the vascular departments of Romodanov Neurosurgery Institute for the period from 1998 to 2019 there were 687 (100 %) patients with AA of vertebrobasilar basin. AA of bifurcation of BA was diagnosed in 210 (30.6 %) patients. The hemorrhagic type of the course of the disease, in the presence of AA of bifurcation of BA occurred in 138 (65.7 %) cases. Asymptomatic unbroken AA of bifurcations of BA were detected in 58 (27.6 %) patients. The pseudotumor type of disease was diagnosed in 12 (5.7 %), ischemic in 2 (0.9 %) patients. Results. The main variants of the clinical course of AA of bifurcation of BA are established. Given the X-ray and anatomical features, certain prevailing for a particular variant of the course of the disease, the most stable characteristics of AA of bifurcation of BA, including the size, shape, neck and the ratio of the height of the dome to the diameter of the neck of AA.Conclusions. According to the results of the study, the main variants of the clinical course of AA of bifurcation of BA were identified: hemorrhagic (65.7 %), asymptomatic (27.6 %), pseudotumor (5.7 %) and ischemic (0.9 %). Localization of AA in the area of BA bifurcation is a rather formidable predictor of a possible hemorrhagic variant of the course of the disease (138 (65.7 %)) out of 210 patients). Based on the analysis of the results of the examination of patients with AA of bifurcation of BA with hemorrhagic disease, it should be considered that convincing factors (predictors) of a possible rupture of AA of bifurcation of BA are its sizes from 4 to 15 mm (81 %) in combination with complex (incorrect) form AA (76 %). With the size of AA of bifurcation of BA 3.0, according to the results of our study, is not a predictor of the hemorrhagic course of AA of bifurcation of BA, in the presence of a narrow neck of AA. In the presence of a small size of AA of bifurcation of BA (