Colorectal cancer is an often fatal cancer with a rapidly increasing incidence. Current mortality is estimated to be approximately 600,000 per year, and both environmental and genetic factors are involved in its etiology. Viral and bacterial factors have a proven role in the incidence of approximately 20% of cancers. In the present study, the Epstein-Barr virus (EBV) was detected in 50 colorectal adenocarcinomas, 12 colon adenomas, and 38 control tissue samples using polymerase chain reaction (PCR). Epstein-Barr virus DNA was identified in 19 of the adenocarcinoma tissues, 1 adenoma tissue and 24 control specimens. In total, 15.8% (3/18) of the colorectal samples in the well-differentiated grade, 79% (15/30) in the moderately differentiated, and 5.2% (1/2) in the poorly differentiated grade tested positive for viral infection. Epstein-Barr virus was more prevalent in the moderately differentiated grade. Statistical analysis did not suggest a significant association between EBV and the incidence of colorectal cancer. However, it appears that the virus stimulates progression of the malignancy.