The aim of this study was to investigate tumor invasion pattern, its heterogeneity and association with histopathological features and stage in invasive urothelial carcinoma of the bladder. We studied 62 cases of invasive urothelial carcinoma of the bladder. World Health Organization ( WHO) 1973, WHO/ISUP 1998 and WHO 1999 systems were used for tumor grading. Pathologic staging of each case was done according to 1997 TNM system. During evaluation of the slides three main tumor invasion patterns were detected: "nodular", "trabecular" and "infiltrative". In addition, homogeneity or heterogeneity of invasion patterns was also recorded for each case. Of sixty-two invasive cases, 17 (27%) had nodular, 36 (58%) trabecular, and 9 (15%) infiltrative invasion pattern. There was a statistically significant difference between invasion patterns in in relation to pathologic stage (pT) (p = 0.001), but not to grade. Of the 17 cases with nodular invasion pattern and 36 tumors with trabecular invasion pattern, 13 (77%) and 26 (72%) were pT1, respectively, whereas 8 of 9 infiltrative cases (89%) were advanced stage (pT2-3). According to heterogeneity, forty-two cases (68%) had homogeneous, while the remaining 20 (32%) had heterogeneous invasion pattern. Of the 42 homogeneous cases 34 (81%) were pT1, whereas 14 of 20 heterogeneous cases (70%) were advanced stage (p = 0.000). The different invasion patterns seem to have a large impact on pathologic stage, especially the infiltrative pattern. In addition, invasion heterogeneity appears to be of value in determination of biologic aggressiveness in urothelial carcinoma.