Feline Leukemia Virus (FeLV) is a retrovirus of the subfamily oncornavirus, which infects domestic cats worldwide. Its complex pathogenicity may include a latent state within its host that may manifest in certain clinical diseases (such as nonregenerative cytopenias) and eludes detection by standard in-house testing (SNAP ELISA on whole blood, serum, or plasma for the p27 antigen). The case of a 1.5-year-old female domestic shorthair cat that presented to Cornell University Hospital for Animals on 2/12/10 for severe anemia represents such a latently infected host and prompts discussion about the pathogenesis of FeLV, various methods of detecting infection, and how to interpret discordant results.