Objective: To report clinical and microbiological features and response to treatment in HIV patients with Rhodococcus equi infection., Design: Retrospective study., Setting: Inpatients admitted to two Infectious Diseases Departments in a community-based hospital., Patients: A total of 12 HIV-positive patients with R. equi infection., Main Outcome Measures: Clinical status, radiological finding, microbiological, haematochemical and immunological tests, and response to treatment., Results: Twelve patients (11 men, six injecting drug users) were diagnosed with R. equi infection. Fever and cough were the principal clinical signs on presentation. Mean CD4+ count at the time of diagnosis was 47.67 x 10(6)/l (SD, 49.2 x 10(6)/l). In 58.3% of the cases the diagnosis of R. equi infection followed the appearance of an AIDS-defining illness. The most frequent radiological findings were cavitary lesions (41.7%) and lung consolidation (33.3%). In 83% of cases, R. equi was isolated from blood and in 33.3% cases from sputum. Test of chemosensitivity showed sensitivity to vancomycin (100%), teicoplanin (100%), ceftriaxone (80%), erythromycin (71%) and ciprofloxacin (66%). Clinical response alone with the disappearance of the presenting signs was observed in nine of the 12 cases (75%); complete response was observed in two cases. Seven patients died with a mortality rate of 58.3% and a mean survival of 5.75 months (SD, 6.48 x 10(6)/l)., Conclusions: R. equi should be considered in the differential diagnosis of pulmonary of disseminated infections in patients with HIV infection. Blood culture may be the most sensitive means of diagnosis. Other studies are needed to determine the most effective choice and duration of antibiotic therapy.