[Thoracic actinobacteriosis due to Actinomyces naeslundii]

The authors report the first case of thoracic actinomycosis due to Actinomyces Naeslundii. A precostal abscess with a large mediastinal and thoracic collection on CT scan was the presenting symptom. Evolution was favorable without sequelae after 6 weeks of Penicillin therapy (10.000.000 U/day).