Abstract： Objective To evaluate the etiology and CT features of thoracic lymphadenopathy in patients with acquired immunodeficiency syndrome (AIDS).Methods CT features of thoracic lymphadenopathy in 178 AIDS patients were retrospectively analyzed.Results Of 668 AIDS patients with thoracic lymphadenopathy,174 were proved to be infections including Penicilliosis marneffei (n =117),tuberculosis (n =42),cryptococcosis (n =10) and non-tuberculous mycobacteria (n =5).Four were proved to be tumors including 3 Kaposi's sarcomas and 1 lymphoma.The enlarged mediastinal and hilar lymph node presented as homogeneous soft-tissue density in 140 patients,with central low attenuation in 29 patients,as extreme low attenuation in 9 patients on plain CT scan and showed homogeneous enhancement in 28 patients,rim enhancement in 19 patients,non enhancement in 2 patients on enhanced CT scan.Accompanied CT findings included diffuse pulmonary micro-nodules (n =45),primary complex or similar primary complex (n =13),pleural effusion (n =59),pericardial effusion (n =24),sandwich sign in the small bowel mesentery (n =31).The CT findings of penicilliosis marneffei and tuberculosis were compared with chisquare test.There were significant differences on homogeneous soft-tissue density,central low attenuation,homogeneous enhancement,rim enhancement,diffuse pulmonary micro-nodules,primary complex or similar primary complex,sandwich sign,pleural effusion (x2 =32.62,43.82,12.13,15.72,11.76,11.06,5.44,4.07,P ＜ 0.05).Conclusions Thoracic lymphadenopathy can be caused by infections and tumors in AIDS.CT plays an important role for the differential diagnosis.