PURPOSE: Actinomycosis is an uncommon chronic granulomatous disease that presents as a slowly progressive, indolent, indurated infiltration with multiple abscesses, fistulas, and sinuses. The purpose of this article is to report on a case of actinomycosis with clinical findings similar to periodontitis. METHODS: A 46-year-old female presented with recurrent throbbing pain on the right first and second molar of the mandible three weeks after root planing. Exploratory flap surgery was performed, and the bluish-gray tissue fragment found in the interproximal area between the two molars was sent for histopathology. RESULTS: The diagnosis from the biopsy was actinomycosis. The clinical and radiographic manifestations of this case were clinically indistinguishable from periodontitis. The patient did not report any symptoms, and she is scheduled for a follow-up visit. CONCLUSIONS: The present study has identified periodontitis-mimicking actinomycosis. Actinomycosis should be included in the differential diagnosis in cases with periodontal pain and inflammation that do not respond to nonsurgical treatment for periodontitis. More routine submissions of tissue removed from the oral cavity for biopsies may be beneficial for differential diagnosis.