The aim of this study was to investigate the existence of any thermal difference between malignant tumors and inflammatory benign lesions of the human urinary bladder and to determine whether it correlates with tumor angiogenesis quantification.A new method, developed in our institute, is introduced to detect temperature in human urinary bladder, in vivo. This method is based on a thermography catheter. We calculated the differences of the temperature of the solid tumor and of a normal area (Delta T) on 20 subjects (mean age, 72.5 years; 95% confidence interval [CI], 68.5 to 76.4). According to the biopsy histology, Eight (40%) patients had benign tumors, and 12 (60%) had malignant tumors.We found significant differences of Delta T between patients with benign and malignant tumor (P <.001). Also, differences were found for the mean values of angiogenesis level between malignant and benign tumors (P =.0261), and a moderated positive correlation was estimated between the degree of angiogenesis and Delta T (P =.02). Based on logistic regression analysis, we found that a 1-degree increase of Delta T triples the odds of a patient having a malignant tumor (odds ratio = 2.91; 95% CI, 1.97 to 7.78; P <.001), adjusted for the degree of angiogenesis (P =.0236) and the grade of tumor (P <.001). A threshold point of Delta T = 0.7 degrees C was determined, with sensitivity 83% and specificity 75%.These findings suggest that the calculated difference of temperature between normal tissue and neoplastic area could be a useful criterion in the diagnosis of malignancy in tumors of the human urinary bladder.