Abstract: Background and Objectives: HIV infection is a global public health problem that can lead to the progression of AIDS. Nutritional status and biochemical markers can significantly contribute to the progression of AIDS in HIV/AIDS patients. The main objective of this study is to examine the association between nutritional and biochemical markers as well as BMI in HIV/AIDS patients in the kingdom of Bahrain. Methods: A retrospective cohort study, including 300 patients (248 males and 52 females) with HIV/AIDS in Bahrain, was carried out. Various biochemical markers were collected from patients’ medical records, including CD4 + T cell count, albumin, Hb, HCT, MCV, WBCs, and creatinine. A semi-structured questionnaire using a standardized food frequency questionnaire (FFQ) was used, from which total energy and total macronutrients were calculated. Results: The mean BMI of the participants was 27.20 kg/m2 , and none of the participants had a BMI lower than 18.5 kg/m2 (underweight). The majority of patients’ dietary intake of macronutrients and total calorie intake were either within or above the recommended RDA levels. The results also showed that all of the mean values of the nutritional and biochemical markers (CD4 + T cell count, albumin, Hb, HCT, MCV, WBCs, and creatinine) were within the normal reference ranges. A significant positive correlation between CD4 + T cell count, Hb, HCT, and albumin at the 0.05 level was found. There was no significant correlation between CD4 + T cell count and MCV, WBCs, and creatinine. A positive significant correlation was found between BMI, CD4 + T cell count, and WBCs at the 0.01 level. Conclusion: The BMI values were significantly correlated with the biochemical markers of AIDS progression. The dietary patterns of the participants were undiversified, with a high prevalence of obesity and overweight. Malnutrition among this study population was not present.