Background Rhodococcus equi (R.equi) infection commonly occurs in grazing areas,especially in patients with AIDS or with T-lymphocyte immuno-deficiencies. Literature reviews revealed that cases radiologically and pathologically diagnosed of AIDS complicated by R. equi infection are rare. This study aimed to investigate the imaging features and pathological basis of AIDS complicated by pulmonary R. equi infection.Methods A total of 13 cases of AIDS complicated by pulmonary R. equi infection were retrospectively analyzed based on their imaging,bacterial culture and pathological data,including 10 cases by chest CT scanning and X-ray radiology and 3 cases by only X-ray radiology. All 13 cases were definitely diagnosed by bacterial culture,including one by CT-guided pulmonary puncture with following H&E staining and periodic acid-Schiff (PAS) staining for diagnostic biopsy and another one by bronchial biopsy with following H&E staining and PAS staining for pathological diagnosis. The imaging findings and the pathological findings of AIDS complicated by pulmonary R. equi infection were compared and evaluated.Results Totally 9 subjects (70%) had radiological demonstrations of central ball liked high density shadows in unilateral pulmonary hilus areas;10 (77%),cavities and liquefied levels;3 (23%),pleural effussion. The foci were found in pulmonary inner zone in 10 subjects (77%) and in pulmonary outer zone in one subject (7%). The pathological findings included intra-alveolar hemorrhage,lymphocyte infiltration and granulation tissue proliferation,which were in line with the pathological process of necrotic pneumonia. After 8-month follow-up of anti-R. equi therapy of these 13 cases,9 cases had obviously decreased or shrunk pulmonary cavities,one died,one missed follow-up,one completely absorbed foci and one did not receive reexaminations.Conclusions The radiological demonstrations of AIDS complicated by pulmonary R. equiinfection are central ball liked high density areas in unilateral pulmonary hilus area,parenchymal changes,secondary cavities,ground glass liked changes in the lung fields,nodules and treeinbuds sign,which are characteristic rather than specific.