Objective — to show the advantages and limitations of urgent morphological diagnosis in oncology. Subjects and methods. In the period from 2017 to 2019, an urgent intraoperative histological examination was performed in 765 patients; an urgent intraoperative cytological examination was conducted in 2.692 patients (24.877 study objects). For urgent histological examination, cryostat sections were used; the specimens were stained with hematoxylin and eosin. An urgent histological examination was carried out for 20—30 minutes. The Leukodif kit (Czech Republic) was used for urgent staining of cytological specimens. It takes 10—15 minutes to make urgent cytological examination. An immunofluorescence study (IFS) using anti-epithelial antigen (Dako Ber-EP4 FITC) was employed to examine exudates from serous cavities and sometimes lymph nodes. IFS was performed on a Carl Zeiss Imager M1 fluorescence microscope. In 2011 to 2017, examinations were made in 218 endobronchial ultrasound guided transbronchial needle aspiration (EBUS-FBNA) samples obtained from 172 patients: without Rapid On-Site Cytological Examination (ROSE) in 178, by applying 40 cases. Results. The significance of intraoperative morphological verification of the diagnosis was 98—99% on histological examination and 95.2% on cytological examination; it might be doubtful in 5% of cases; the impossibility of deciding whether the process was malignant was in 1%. Examinations of sentinel lymph nodes (SLN) in breast cancer (BC) showed a sensitivity of 95.7%, a specificity of 99.7%, a significance of 99.1%, and an effectiveness of 93.1%. Urgent cytological study of SLN in early BC revealed macrometastases in 71% of cases. Micrometastases accounted for 16% of all histologically detected metastases, of which only 23% of all micrometastases had been cytologically detected. SLN metastases were seen in 5% of melanomas. When materials were adequately sampled, the accuracy of urgent intraoperative diagnosis in clarifying the extent of the tumor process was 97—98%. ROSE (to explain what it was?) during EBUS-TBNA showed a sensitivity of 96%, a specificity of 100%, and an accuracy of 98%. The effectiveness without ROSE was 76%; that with ROSE was 80%. ROSE could specify the stage of the tumor process in 40% of patients. Conclusion. The importance of urgent intraoperative morphological diagnosis in oncology is undeniable, since it is an effective method and contributes to adequate surgical treatment, which is the key to long-term disease-free survival. Currently, there is a general tendency to reduce tissue resection volumes in compliance with the principles of cancer safety, which improves quality of life in patients and does not worsen disease prognosis, so the number of intraoperative morphological studies is on the rise. Of particular relevance is the intraoperative study of SLN in BC and melanoma, as well as that of resection margins in BC. ROSE is also extremely relevant to morphologically verify the masses that are hard to reach using minimally invasive techniques.