Background:Actinomycosis is a rare indolent infectious disease caused by Actinomyces.Although pulmonary actinomycosis is thought to be more prevalent in developing countries,data from developing countries are scanty.This study was to reveal the current situation of pulmonary actinomycosis in developing countries and the difference from that in developed countries.Methods:Patients fulfilling the inclusion criteria for pulmonary actinomycosis from Peking Union Medical College Hospital in China between January 2003 and December 2014 were retrospectively analyzed.Baseline characteristics,clinical symptoms,underlying diseases,diagnostic methods,pulmonary function test results,chest computed tomography (CT) tests,fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) tests,initial diagnosis,treatment and prognosis were retrieved from medical records and analyzed.Results:Twenty-six patients were included in this study (mean age 52.0 + 13.1 years).The ratio of male to female was 1.17:1.Most common clinical symptoms were cough (15/26),sputum (12/26) and hemoptysis (12/26).Chest CT findings presented as masses (13/26),nodules (10/26) and infiltrates (3/26).FDG-PET had an increased standardized uptake value and 4/6 patients were misdiagnosed as malignancy.Many kinds of antibiotics were used in the treatment of pulmonary actonomycosis and all got favorable results.Five patients receiving complete resection of the lesion were cured without postoperative use of antibiotic.Conclusions:Pulmonary actinomycosis is a rare disease even in developing countries,and both misdiagnosis and missed diagnosis are common.FDG-PET seems useless in the differential diagnosis,and complete resection of the pulmonary lesion without postoperative antibiotic therapy might be enough to achieve cure.