Background: Bladder cancer (BC) is an aggressive disease that begins in the cells lining the bladder, which grows abnormally due to mutations. One of the aggravating factors during treatment is the nutritional risk, contributing to increased morbidity and mortality. Nutritional screening can be extremely important for these patients since the nutritional condition can deteriorate during treatment and due to the progression of the disease. Objectives: This cross-sectional observational study aimed to compare the results of using the Mini Nutritional Assessment (MNA) nutritional screening tool obtained by urologists and nutritionists at our center. Methods: The target audience were adult patients diagnosed with BC. They were followed up at the urology outpatient clinic and were asked to answer the questions in the short version of MAN during a nutritional screening conducted by a medical team, and later answer the questions contained in the full version of the instrument during a nutritional consultation by nutritionists. The data were analyzed and organized by employing a RedCap database. Statistical analysis of data was performed using the SPSS software package. For comparison between continuous variables, the Mann–Whitney U-test and Student’s t-test were utilized. For analyses of the categorical variables, the Wilcoxon Matched Pairs test and the Cohen Kappa test were used. A significance level of 5% (P ≤ 0.05) with a confidence level of 95% was set for all statistical tests. Results: A total of 46 patients were evaluated. The medical team identified 18 (39.1%) with normal nutritional status, while the nutrition team identified 13 (28.3%). In comparison, the use of the full version of the MNA administered by the nutrition team found that 32 (69.6%) patients were at nutritional risk. Individual questions of the short-version MNA were also compared between the two groups and the Wilcoxon Matched Pairs test was performed. The short-version MNA was found to be an excellent screening tool. When applied by a urologist, it yielded a sensitivity of 87.5% (P = 0.87) and a sensitivity of 93.7% (P = 0.76) when used by the nutritionist. A raw match rate was 71.7% achieved by both questionnaires, and the Cohen Kappa test showed that the agreement was moderate, with an agreement rate of 77.9% (k = 0.50). Conclusion: The application of short-version MNA has a high sensitivity. However, the full-version MNA is necessary for nutritional screening to improve the sensitivity of the assessment and to serve as a guide for nutritionists and the multidisciplinary care team.