We report 4 cases of osteitis with extensive necrosis of the maxillofacial bone due to actinomycosis. Histological study showed soft tissue necrosis with bone involvement, suppuration and granulomatous inflammation. At contact with bone destruction, numerous Gram and PAS positive bacteria with branched filaments, inconsistently associated with granules, were noted. Cultures were negative. Ultrastructural study showed in two cases, some elongated bacteria, variable in size, less to one micron in diameter, associated with ossein destruction. Actinomycetes usually represented in the normal oral flora, may become pathogenic in debilited host. Histologic study is necessary for the diagnosis allowing to confirm the tissue invasion by the bacteria.