Thoracic actinomycosis is an uncommon bacterial infection characterized by its ability to spread to contiguous tissues without regard to normal anatomic barriers. Together with the reduction of its incidence, the clinical presentation has changed markedly over the past decade. Nowadays, extensive destruction of the chest wall is rarely seen. We report a patient who was admitted with a soft tissue mass on the left lateral chest wall. Radiography and CT scans of the chest showed lower left lobe consolidation with fluid collection and extension to the pleura, chest wall, and retroperitoneum. Pulmonary actinomycosis was confirmed by operation and pathology. Treatment consisted of surgical resection, drainage, and antibiotics.