Polymerase chain-reaction procedure was used to test archival samples of prostate tissue from 90 cancer patients for cytomegalovirus infection detected in 46.7%. The median Gleason score and G-index (TNM classification) were significantly higher in CMV-positive patients (8 and 4, respectively) than those in CMV-negative ones (6 and 2, respectively). A relationship between cytomegalovirus infection and poor prognosis of prostate cancer is suggested.