Viral infections in renal transplant recipients are essentially opportunistic. They are dominated by Herpesviridae infections, mainly Cytomegalovirus and Epstein-Barr virus, viral hepatitis, BK virus and Adenovirus nephropathies. They present themselves in the form of primary infection or reactivation of a latent virus in the recipient. Their clinical manifestations and consequences are of variable severity, depending on the tropism and pathogenicity of the virus, but also on the depth of the patient's immunodepression. The microbiology laboratory plays a central role in this context and the development of molecular biology has improved the diagnosis and follow-up of these infections. Virological diagnosis involves serodiagnosis, viral culture and/or the detection of viral antigens or their nucleic acids in tissues or biological fluids by real-time quantitative PCR techniques. Prevention and treatment of these infections are based on vaccination, antiviral chemoprophylaxis, monoclonal antibodies and adaptation of immunosuppressive therapy.