Introduction. Despite significant advances in prevention, chemotherapy-induced (cytostatic therapy) nausea and vomiting (CINV) continues present a significant clinical problem for patients oncohematological profile, while often remaining outside areas of attention of pediatric oncologists and hematologists.The aim of the study – frequency comparison of occurrence CINV according to data obtained from the medical database documentation (retrospective group) and data obtained in the process assessment of CINV using a modified questionnaire and specialized scales (prospective group).Materials and methods. The retrospective group included 52 patients who received 178 cycles of highly emetogenic anticancer therapy with standard antiemetic prophylaxis from 02/01/2020 to 08/01/2020, in prospective – 88 patients who received 456 cycles of a similar anticancer therapy with standard CINV prophylaxis from 10/01/2020 until 07/01/2021.Results. Although the groups were comparable in terms of key patient characteristics, chemotherapy regimens, and regimen prevention of CINV, the frequency of complete control of CINV between them is significantly was different: when analyzing the primary documentation, it turned out that the complete control of CINV in the acute, delayed and general periods is observed in 82 %, 86 %, 82 % cycles, while when assessing CINV using specialized questionnaires, the absence of these complications was noted only in 68 %, 52 %, 43 % of cycles. Thus, if we focus on standard tools fixing complications (diary entries, prescription lists), in more than 80 % of children receiving highly emetogenic cytostatic therapy it is possible to achieve complete control of CINV, and this complication does not really pose a clinically significant problem. However, when using a questionnaire and specialized scales, it becomes obvious that that more than half of children continue to suffer from CINV despite the standard prophylaxis of this complication.Conclusion. In this way, the analysis performed shows that the frequency of development of CINV during routine antiemetic prophylaxis is clearly underestimated, and, in part, due to this CINV and remains outside the attention of pediatric oncologists and hematologists. For an adequate assessment of the true incidence of CINV and, accordingly, determining the need for improvement of existing approaches to their prevention, a key role should be played specialized questionnaires and scales that fully allow “visualize” this complication.