Actinomyces is a genus of gram-positive anaerobic or microaerophilic bacteria that colonize the upper respiratory and gastrointestinal tracts and the female genital tract. These organisms cause disseminated disease in the mouth, the respiratory system, and rarely in the gastrointestinal tract. The diseases produced by Actinomyces species result from the disruption of the barriers that allow the dissemination of the bacteria through the surrounding tissues. The appendix is often a nidus of Actinomyces infection, but a prompt diagnosis cannot be made without the results of histologic examination of the appendix. The treatment of choice for actinomycosis of the appendix is the high-dose parenteral administration of penicillin G for 2 weeks immediately after the diagnosis has been made and continued oral treatment with that agent for at least the next 6 months. We present the case of a 13-year-old adolescent boy with actinomycosis of the appendix that was identified by histologic examination after appendectomy.