Actinomycosis is a relatively rare infection. This is a report of 16 patients with pulmonary actinomycosis diagnosed from 1990 to 1997 at the Central Chest Hospital, Thailand. Twelve patients were male and 4 were female, with a mean age of 59 years and a mean duration of symptoms of 9 months. Common symptoms were cough and hemoptysis. Mass-like shadowing was the most common radiographic finding (37%). The diagnosis, based on findings of typical sulfur granules, was reached by bronchoscopy (10 cases), surgery (5 cases) and fine needle aspiration (1 case). Endobronchial mass with luminal occlusion was the most frequent bronchoscopic finding (56%). Coexistent bronchial carcinoma was present in one specimen. Penicillin was given in 10 patients, 2 of whom (20%) were cured, 5 (50%) are currently on treatment and have achieved clinical response, whereas, the other 2 patients (20%) did not respond. Surgical resection was performed in 8 patients, all of whom recovered. An awareness of the full spectrum of actinomycosis manifestations will expedite diagnosis and optimize treatment.