Appendiceal spirochetosis is rarely described in the literature. We assessed the incidence of spirochetosis in a series of 109 appendectomies (76 adult and 33 pediatric cases) done for either suspected acute appendicitis or as a concurrent procedure. Appendiceal spirochetosis was identified on hematoxylin-eosin sections and confirmed by Steiner and Steiner stain and ultrastructural study in two women and two men. One of these four patients was found to have HIV infection. The HIV status of the other three patients was unknown. We observed appendiceal spirochetosis to be an uncommon phenomenon that affects both sexes, occurring with or without symptoms of acute appendicitis. None of our four positive cases occurred in the pediatric age group.