Introduction. Compound odontoma is an abnormal development of dental tisssue which is characterized by regular and ordinate structures that resemble a normal tooth. Actinomyces is an abnormal inhabitant of the oral cavity which is able to become pathological whenever the specific or non specific defense mechanisms of an individual may fail. Materials and methods. Described is a case of 60 years old male with no deficit of his immune system confirmed by various analysis. There is one year history of an intermittent pain to the left half of his mandible. An x-ray suggests an odontoma. The gengiva, near the lesion, appears to be ulcerated; two fistulous tracts with the oral mucosa and one with the skin area are seen. After decalcification the tissue obteined from the lesion has been fixed in formalin and included in paraffine. The slides were stained with Haematoxilin-Eosin, PAS and Grocott's silver method. Results. The lesion consists of well differentiated enamel and dentin including a fragment of the pulp featuring the typical aspects of compound odontoma. In addition the pulp shows an intense infiltration of granulocytes, plasma cells and numerous capillaries; around the pulp an extensive area of necrosis is present, in which there are eosinophilic aggregates of amorphic and granular matrix suggestive of an infection by actinomyces. This was confirmed with PAS and by an intense argyrophilia. Conclusion. Described is a case of compound odontoma complicated by an actinomycosis infection in a patient with a well functioning immune system which appears to be the first case reported in the literature, to the best of our knowledge.