The most frequent mechanism of paradoxical air embolism is the shunting of blood through a patent foramen ovale (PFO), the frequency of which in the general population is significant and is about 27.3%. The frequency varies depending on the associated condition or disease. The incidence of PFO in neurosurgical patients varies and may be significantly lower according to some authors. Objective — to determine the occurrence and severity of PFO in patients scheduled for neurosurgery. Material and methods. Transesophageal echocardiography with «bubble» test and Valsalva maneuver was performed in patients after anesthesia induction and trachea intubation. Results. A total of 72 people were included in the study. In 5 of them the test was considered unsatisfactory. PFO was detected in 69% (95% CI 57—80). At the same time, it was significant in 25% (95% CI 15—36) of them. Only 7% of the cases could be determined using the color doppler in the absence of the Valsalva maneuver. The total time spent on the diagnosis of the PFO was 12 (10; 18) minutes. Conclusions. The incidence of PFO in patients who are scheduled for neurosurgery is 69% (95% CI 57—80), with 25% (95% CI 15—36) of which are significant.