The aim of the work: to compare the treatment response assessment in a patient with colorectal cancer liver metastases using RECIST 1.1 criteria and volumetric analysis. Materials and methods. A clinical case of a 65-year-old male (born in 1955) with histologically confirmed colorectal adenocarcinoma and multiple liver metastases is presented. From 2020 to 2022, nine series of contrast-enhanced multislice computed tomography were performed. Analysis was carried out according to RECIST 1.1 (linear measurements of target lesions in segments S3 and S7 of the liver) and by volumetric method (calculation of total tumor volume after three-dimensional reconstruction). Descriptive statistics were applied. Results. According to RECIST 1.1, partial response was recorded in 2020, followed by stable disease during the first half of 2021 and progression at the end of 2021–2022. Volumetric analysis demonstrated more pronounced changes: regression of total tumor volume from 919.5 cm³ to 265.3 cm³ by December 2020, stabilization in early 2021, and early signs of progression already in August 2021, with subsequent increase to 888.8 cm³ by June 2022. The findings revealed that volumetric analysis allows earlier and more accurate detection of both regression and progression of tumor burden compared to RECIST 1.1. These results are consistent with recent studies. Despite the need for standardization and higher resource requirements, volumetry has significant potential for integration into clinical practice. Conclusion. Volumetric method provides a more informative assessment of tumor dynamics compared to RECIST 1.1 and may serve as an additional tool for monitoring treatment effectiveness in patients with colorectal cancer liver metastases.