Human cytomegalovirus is a herpes virus that causes latent infections with a possibility of reactivation. Viral proteins and HHV5 nucleic acids have been found in tissues of numerous malignant tumors such as glyoblastomas, medulloblastomas, neuroblastomas, rhabdomyosarcomas, breast carcinoma, colorectal carcinoma, etc. HHV5 is not regarded as oncogenic virus, but rather as a virus that takes part in process known as “oncomodulation”. Activity of its proteins and noncoding RNAs influence proliferation, survival, invasion and immunogenicity of tumor cells and production of angiogenic factors. Despite the fact that many researches have been done on this topic, the process of oncomodulation is not fully understood. It is necessary to standardize sensitive techniques to detect infection, but one of the central aims remains to be development of therapeutic strategies that will prevent HHV5 replication or target its regulatory proteins and noncoding RNAs.