Background: HIV can interrupt the normal development of bone marrow cell lines. Bone marrow aspiration/biopsy (BMA/B) has been described as a diagnostic tool in AIDS patients with fever of unknown origin (FUO). In this review, we aimed to study patients with AIDS who had undergone a BMA/B to investigate FUO and describe the pathologies diagnosed in the biopsy. Methods: Thirty-four BMA/B samples were collected from AIDS patients admitted for work-up of FUO to the infectious disease ward of a tertiary referral HIV center in Tehran, Iran, between September 2014 and September 2015. Data including age, sex, duration of disease, CD4 cell counts, hepatitis B (HBV) and C (HCV) coinfection, the primary presentation of AIDS, and the treatment history were retrieved and analyzed. Patients underwent BMA/B. An expert pathologist reviewed the BMA/B specimens. Results: The mean age of the patients was 37.5 years (range, 26-56), and 27 (79%) were men. Twenty-seven (79%) patients contracted HIV from injection drug use, and 7 (21%) via sexual transmission. Only 3 (9%) of the BMA/B examinations were normal. Hypocellular bone marrow was diagnosed in 22 (65%) patients. Other pathologies included granulomas in 6 (18%), hematologic malignancies in 2 (6%), and leishmaniasis Aspergillosis, each in 1 (3%) patient. Six (17%) of the specimens were found to have tuberculosis infections. Conclusion: Hypocellular bone marrow was the most common pathology on BMA/B examinations, followed by the presence of granulomas. Tuberculosis, Aspergillosis, and Leishmaniasis the opportunistic infections diagnosed on BMA/B specimens. Our results support BMA/B as an appropriate diagnostic tool for early diagnosis of opportunistic infections and malignancies in AIDS. BMA/B is indispensable in the armament of diagnostic tools of the physicians managing AIDS patients.