Objective: The current study determines the causes of mortality in cases of human immunodeficiency virus/ acquired immunodeficiency syndrome (HIV/AIDS) in a developing country where there is no difficulty in accessing antiretroviral therapy and to determine the measures that can be taken to reduce mortality. Methods: The study was conducted between 2003 and 2018. Patient data were extracted from patient files until 2007 and, after that date, from patient files and hospital information software. The cause of mortality was determined based on the patients’ complaints at admission, clinical, radiological, microbiological, and pathological findings. The causes of mortality were studied in three groups as “HIV-related”, “HIV-associated” and “other.” Results: The study enrolled 31 (10.8%) cases resulting in mortality from 287 patients followed up in our outpatient clinic. The average age of the cases was 47 (25-68) years and 27 (90%) of them were men. The cause of death of most of our patients was opportunistic infections, notably disseminated tuberculosis. Among the malignancies, AIDS-defining ones such as lymphoma and Kaposi's sarcoma were identified as the most common causes of death. Conclusion: Deaths were most frequently caused by “HIV-related” causes such as AIDS-related opportunistic infection and AIDS-defining malignancies. For an early diagnosis of HIV/AIDS, more efforts should be made to screen risk groups and keep diagnosed patients in follow-up and treatment.