An 18-yr-old female captive-born chimpanzee (Pan troglodytes) presented with an intermittent history of inappetence, lethargy, and lower limb stiffness. No notable abnormalities were found on exam or complete blood cell count and serum biochemistry analysis. Serologic testing was strongly positive via indirect fluorescent antibody testing and Western blot for Borrelia burgdorferi. Treatment with doxycycline was initiated, and a clinical response was seen within 1 wk. Convalescent serum exhibited an eightfold increase in titer. Serologic testing was performed on several conspecifics with banked serum; while some low positive titers were present and presumed indicative of past exposure, no titer was elevated to the extent of the affected chimpanzee during its course of disease. To the authors' knowledge, this is the first report of suspected Lyme borreliosis in a great ape species, and the case originates from an area of the United States with a high incidence of human borreliosis.