Introduction: The purpose of this study is to determine mid arm circumference as a predictor of nutritional status and prognosis of hospitalized patients diagnosed with acquired human immunodeficiency syndrome. Methods: Cross-sectional study with a quantitative approach involving hospitalized patients with acquired human immunodeficiency syndrome. Clinical, nutritional, biochemical, sociodemographic and anthropometric data were collected, based on information in medical records and follow-up forms. Data were statistically analyzed according to the nature of their variables, using Minitab® software. Normality was seen from the Kolmogorov-Smirnov test. Spearman’s rho (r) and Pearson’s chi-square (χ2) tests were applied for correlation and association, respectively. The reliability of the arm circumference was evaluated from the precision measures and its reproducibility was measured by the Kappa coefficient. Results: The sample consisted of medical records of 95 patients, with an age range predominantly between 18 and 45 years, comprising about 80% of the sample universe. Approximately 70% of the sample presented malnutrition by arm circumference. Individuals who received this diagnosis had an increased risk of developing hypoalbuminemia, high C-reactive protein, high Rits Index, and greater chances of developing an inadequate caloric and protein intake (p<0.05). The arm circumference showed an excellent negative likelihood ratio value (VR- = 0.11), despite modest accuracy. The value of the kappa coefficient demonstrates a moderate agreement between the malnutrition classification by arm circumference and the classification by body mass index. Conclusion: Mid arm circumference can be used as a predictor of the nutritional status and prognosis of patients with acquired human immunodeficiency syndrome in hospital follow-up.