This chapter highlights the neurologic sequelae of viruses from two major groups of arenaviruses, the Lassa-lymphocytic choriomeningitis serocomplex and the Tacaribe serocomplex. Fundamental features of these viruses are reviewed, including the rich history of their discovery and the large influence that the study of arenaviruses has had on the disciplines of virology and immunology more generally. Virus morphology, viral genome organization, individual viral protein functions, and small-animal models of disease are also discussed. The epidemiology, natural history, and laboratory evaluation of the arenaviruses that cause human illness are presented. In particular, the neurologic complications of lymphocytic choriomeningitis virus in immunocompetent, pregnant, and solid-organ transplant patients are highlighted. The neurologic sequelae of the arenaviruses that cause hemorrhagic fever (i.e., Lassa fever, Argentine hemorrhagic fever, Bolivian hemorrhagic fever, Venezuelan hemorrhagic fever) are also presented. Lastly, potential treatment and vaccine strategies of these diseases are reviewed. © 2014 Elsevier B.V.