Lymphocryptoviruses (LCVs) have been identified as naturally occurring infections of both Old and New World nonhuman primates. These viruses are closely related to Epstein-Barr virus (EBV, Human herpesvirus 4) and share similar genomic organization and biological properties. Nonhuman primate LCVs have the ability to immortalize host cells and express a similar complement of viral lytic and latent genes as those found in EBV. Recent evidence indicates that nonhuman primate LCVs can immortalize B cells from genetically related species, suggesting a close evolutionary relationship between these viruses and their respective hosts. Early work with EBV in tamarins and owl monkeys revealed that cross species transmission of lymphocryptoviruses from the natural to inadvertent host may be associated with oncogenesis and the development of malignant lymphoma. Moreover, simian LCVs have the ability to induce malignant lymphomas in immunodeficient hosts and have been associated with posttransplantation lymphoproliferative disease in cynomolgus macaques undergoing solid organ transplantation. This review will focus on the comparative pathobiology of lymphocryptoviral infection and discuss the derivation of specific pathogen-free animals.