There are four cases of Actinobacillus actinomycetemcomitans pulmonary infections reported in the English literature prior to 1990. We report a case of A actinomycetemcomitans pulmonary infection with invasion of overlying soft tissue, rib, and sternum. This manifestation has not been previously reported. The clinical manifestation is similar to that of Actinomyces israelii, which may be misinterpreted as malignancy initially. The portal of entry of A actinomycetemcomitans may be via hematogenous spread or aspiration. The diagnosis depends on culture after prolonged incubation of the involved tissue obtained by aspiration or biopsy. Elevated serum antibody is helpful for diagnosis of active infection. A actinomycetemcomitans is susceptible to most antibiotics, but is frequently resistant to penicillin, vancomycin, clindamycin, and erythromycin. Isolation of the organism and an in vitro drug sensitivity testing are important in managing the patient. Our patient recovered after a three-month regimen of penicillin.