Actinomycosis is an infectious disease that frequently has chronic granulomatous and suppurative lesions caused by saprophytic Actinomyces species. Although cervicofacial actinomycosis is known to be the most common type, intraorally and periodontally types occur rarely in a localized fashion. The present case reports on an adult periodontitis patient with a diffuse and atypic actinomycotic lesion which was limited to the gingiva and had an abscess formation, a large desquamation and subsequent exposure of the alveolar bone in the involved region. Diagnosis was based on histopathological examination, the history of the case and clinical nature of the lesion. The patient responded to daily administration of 100 g doxcycycline (first day-bid) for 3 weeks and 0.2% chlorhexidine gluconate irrigation (following tooth brushing) performed with oral hygiene reinforcement and periodontal debridement procedures. Complete improvement of the lesion was observed after 5 weeks. Due to the opportunistic characteristics of the actinomycotic infection, early and adequate differential diagnosis of actinomycosis prior to therapeutic attempts, as well as management steps, are of great importance in the oral cavity to prevent the spread of the disease.