ABSTRACTActinomycosis is a chronic, suppurative bacterial infection characterized by multiple abscesses, sinus tracts, fibrosis, and granulation involving the face, neck, thorax and abdomen due to an anaerobic gram positive commensal bacteria, harbored in the healthy cavities. Primary actinomycosis of the lung is a rare disease and probably results from aspiration of oropharyngeal secretions. Without characteristic clinical signs, may present as chronic respiratory, disease with abnormality of radiography. Approximately 90% of patients have undergone diagnostic and therapeutics procedures based on a wrong diagnostic hypothesis. The authors present a comprehensive review of thoracic actinomycosis apropos of three clinical cases. One case was suspected as lung tumor, the second case was consider as recurrence of lung malignancy, and the third case present as recurrent pneumonia after foreign body aspiration in airway. Final diagnosis was confirmed by histology examination.REV PORT PNEUMOL 1999; V (3): 341-348