Objective. To determine the detectability of foci of acute ischemic stroke (AI) using neuroimaging methods depending on the localization, timing and severity of stroke. Material and methods. A retrospective evaluation of 100 case histories of patients hospitalized for ischemic stroke (IS) with determination of the timing of neuroimaging study, fibrinogen level, glucose, INR, NIHSS scores on admission to the hospital, assessment of stroke localization (hemispheric or brainstem), the severity of atherosclerosis of the brachiocephalic arteries (BCA) and presence of atrial fibrillation (AF) was performed. During the stay in the hospital, 54 patients were re-examined to clarify the diagnosis. All patients were divided into 2 groups: patients with the focus of AI revealed on primary neuroimaging study (group 1) and patients with the focus of AI at repeated neuroimaging or patients without lesions on CT or MRI (group 2). Results. Stem strokes were dominated in group 2. An increase in glucose above 10 mmol/l was more often detected in group 1 (p<0.05). AF was detected in 13 patients of group 1 and 9 of group 2. NIHSS <10 values were detected in 8 patients of group 1 and 3 patients of group 2 (p<0.05). An occlusive BCA lesion was found only in patients of group 1(n=4). Conclusion. Cases of AI not detected by CT/MRI on admission to the hospital are more common in women, have stem localization, characterized by low values of NIHSS and lower glucose levels on admission to the hospital.