Objective In The Paris System for Reporting Urinary Cytology (TPS), the important cytomorphological features for diagnosing high‐grade urothelial carcinoma (HGUC) are a nuclear‐to‐cytoplasmic (N:C) ratio exceeding 0.7, hyperchromasia, coarse chromatin, and irregular nuclear borders. However, quantitative cytomorphological assessments of HGUC cells using SurePath slides are rare. Therefore, we evaluated HGUC cells on SurePath slides quantitatively using a digital image analysis system and compared these data with ThinPrep data. Methods The same urine samples were divided into two aliquots and used to prepare SurePath and ThinPrep slides. We used ImageJ to measure the N:C ratio, hyperchromasia, and irregular nuclear borders for HGUC cells on SurePath and ThinPrep slides. Results The total number of analysed HGUC cells on SurePath slides was 981, versus 889 on ThinPrep slides. Hyperchromasia and irregular nuclear borders were significantly more severe on SurePath than on ThinPrep slides. Conversely, the N:C ratio did not differ between the methods. Additionally, HGUC cells with N:C ratios exceeding 0.7 were present on almost all slides for both methods. Conclusions Our data indicated the reasonableness of using the N:C ratio as the major criterion for TPS on both SurePath and ThinPrep slides, and an N:C ratio cut‐off of 0.7 as suitable for identifying HGUC cells. However, the severity of hyperchromasia and irregular nuclear borders differed between the processing methods. Our study indicated the reasonableness of using the N:C ratio as the major criterion for The Paris System for Reporting Urinary Cytology on both SurePath and ThinPrep slides. However, the severity of hyperchromasia and irregular nuclear borders differed between the processing methods.