Pulmonary actinomycosis is a rare disease. Of 2,247 patients presenting with a radiological pulmonary opacity, 13 (0.6%) were identified with pulmonary actinomycosis in a 13 year period. Twelve of the 13 patients underwent thoracotomy and one had clinical diagnosis and subsequent medical treatment alone. Neither mortality nor major complications were observed. One patient had recurrent disease after surgery. The other surgical patients are well and free from disease at a minimum 6 month follow-up. Diagnosis of actinomycosis is frequently difficult because it often infects pre-existing cavitary disease in the lung. As a consequence, the infection may progress to stages which will not respond to medical treatment alone. Surgery then provides the best method to achieve diagnosis and ultimate treatment.