Objective: This study was designed to investigate differential pattern of G1-cyclins (D1 and E) in transitional cell carcinoma (TCC) of human urinary bladder with or without human papillomavirus-18 (HPV-18) infection. Methods: Immunohistochemistry method was used in the detection of the expression of G1-cyclins in 57 cases of TCC (7 normal bladders as control), and HPV-18 DNA was found in 29 cases by polymerases chain reaction (PCR). Results: Cyclin D1 expression was found in 41 of 57 (71.93%) TCCs and it was reverse associated with HPV (x2=8.21, P 0.05). Cyclin E expression was found in 17 of 29 (56.82%) in HPV-18 infection group and 19 of 28 (67.86%) in non-HPV infection group. There was obvious difference in the cyclin D1 and cyclin E expression between the TCC and normal tissue (x2=7.46, P<0.05; x2=7.45, P<0.05, respectively). Conclusion: These data demonstrated that HPV infection altered the control of G1 cell cycle. And changes of G1 cell cycle regulatory proteins, either by interaction of cellular protein with viral oncoproteins or by changes in the cellular proteins themselves, may be critical for carcinogenesis of TCC of urinary bladder.