Bladder cancer is the second most commonly occurring genitourinary cancer in adults. The interaction of different carcinogenic and cocarcinogenic agents are responsible for bladder urothelial carcinoma: alcohol and smoking habits, Schistosoma haematobium infection, exposition to chemicals, analgesic and antineoplastic drugs prolonged use. Recently also viral infections have been associated to this pathology. In this study the correlation between viral infections and bladder carcinoma has been evaluated. A group of 32 patients affected by primary bladder neoplasia has been analysed. A control group of 20 autoptic samples of healthy bladder was analysed. The DNA of the following viruses has been searched by polymerase chain reaction (PCR): Adenovirus, Herpes simplex virus type 1 (HSV-1), Herpes simplex virus type 2 (HSV-2), Human Papillomaviruses (HPV), Polyomaviruses (BKV and JCV). In the examined population the association bladder carcinoma-HPV, found by others, has not been confirmed. The high percentage of human polyomaviruses present in the samples is a statistically significant data (p=0.0087) and allows to presume that BKV and JCV may play a role in the aetiology of bladder tumor. In particular the polyomavirus BK, which is found in significative percentage both in single infection (p=0.0036) and in co-infections with other viral species (p=0.035), may be an important co-factor in the pathogenesis of bladder carcinoma.