In the center of the septum which separates the right from the left atrium (interatrial septum) there is a slight depression and immediately below there is the foramen ovale, which may sometimes remain open even after birth. Patent foramen ovale (PFO) has become more easily detectable after the introduction of transesophageal echocardiography (TEE), and it has been proven in various percentages to be a risk factor especially in cerebrovascular events. In this study we aimed at investigating PFO incidence in patients with cerebrovascular events or subjected to TEE for other indications, and at determining the involvement of cerebral emboli. The study group consisted of 2176 patients (913 males - 42%, and 1263 females - 58%, mean age 48.9 ± 17.3 years, range 14-89 years) who had cerebrovascular events and/or had been subjected to TEE for other indications. A contrast procedure was performed in each case. Agitated saline was used as contrast substance. Seven hundred and forty-four patients with rheumatic valve disease were excluded from the study. The remaining 1432 patients, 672 males (46.7%) and 760 females (53.1%), were divided into four groups: Group 1 (55 patients, 21 males and 34 females, age range 14-40 years) subjected to TEE due to cerebrovascular events and emboli; Group 2 (219 patients, 120 males and 99 females, age range 41-89 years) subjected to TEE due to cerebrovascular events and emboli; Group 3 (431 patients, 166 males and 265 females, age range 14-40 years), taken as control group, subjected to TEE for various reasons, and Group 4 (727 patients, 365 males and 362 females, age range 41-89 years), taken as control group, subjected to TEE for various reasons. PFO was found in 117 out of 1432 (8.2%) patients (12 in Group 1, 13 in Group 2, 44 in Group 3, and 48 in Group 4). No significant statistical difference was observed between Group 2, which consisted of stroke patients, and Group 4, whereas there was a significant difference between Group 1 and Group 3 (p < 0.02), and between Group 1 and Group 2 + Group 3 + Group 4 (p < 0.00044). The relation between mitral valve prolapse, atrial septal aneurysm, mitral annulus calcification, and aortic plaques, which are frequently associated with PFO and young age strokes, was evaluated. PFO and mitral valve prolapse occurred concomitantly in 20 patients, 5 of whom (25%) with earlier cerebrovascular event. In those cases in which PFO and mitral valve prolapse were concurrent, young age stroke was significantly higher (p < 0.005). PFO + atrial septal aneurysm, PFO + mitral annulus calcification, and PFO + aortic plaque occurrences did not enhance the risk of young age stroke. The incidence of PFO among nonvalvular cases was 8.2%, whereas in the young age stroke group was significantly high. In patients for whom TEE has been indicated it will be necessary to investigate the etiology and perform the contrast procedure in order to prevent a possible future emergence of the condition and direct treatment.