Callitrichid hepatitis is an infection of New World primates caused by an arenavirus, currently referred to as callitrichid hepatitis virus, that is closely related to lymphocytic choriomeningitis virus (LCMV). We have cloned and sequenced the GP-C gene of callitrichid hepatitis virus and found that the cDNA sequence is 84 to 86% identical to those of the GP-C genes of LCMV strains Armstrong and WE, while the deduced amino acid sequence is 95 to 96% identical to those of the GP-C gene products of the same strains. This high degree of similarity indicates that the etiologic agent of callitrichid hepatitis is in fact LCMV. The wide geographic distribution of callitrichid hepatitis outbreaks in the United States serves as a reminder that LCMV is also a human pathogen whose public health implications are not well understood.