The prostate tumor overexpressed-1 (PTOV1) protein was first described overexpressed in prostate cancer but not detected in normal prostate. PTOV1 expression is associated to increased cancer proliferation in vivo and in vitro. In prostate biopsy, PTOV1 detection is helpful in the early diagnosis of cancer. The purpose of this study was to analyze the relevance of PTOV1 expression to identify aggressive tumors derived from 12 different histological tissues. Tissue microarrays (TMAs) containing 182 biopsy samples, including 168 human tumors, were analyzed for PTOV1 and Ki67 expression by immunohistochemistry. Tumors of low and high histological grade were selected from lung, breast, endometrium, pancreas liver, skin, ovary, colon, stomach, kidney, bladder, and cerebral gliomas. One TMA with representative tissues without cancer (14 samples) was used as control. PTOV1 expression was analyzed semiquantitatively for the intensity and percentage of positive cells. Ki67 was evaluated for tumors proliferative index. Results show that PTOV1 was expressed in over 95% of tumors examined. Its expression was significantly associated to high-grade tumors (p = 0.014). This association was most significant in urothelial bladder carcinomas (p = 0.026). Overall, the expression of Ki67 was associated to high-grade tumors, and it was significant in several tumor types. PTOV1 and Ki67 were significantly co-overexpressed in all tumors (p = 0.001), and this association was significant in clear cell renal carcinoma (p = 0.005). In conclusion, PTOV1 expression is associated to more aggressive human carcinomas and more significantly to bladder carcinomas suggesting that this protein is a potential new marker of aggressive disease in the latter tumors.