BACKGROUND: In HIV-medicine, the Veterans Aging Cohort Study (VACS) index is associated to some geriatric syndromes and has also been recently used as a proxy of frailty. However, using it as a proxy for the frailty phenotype may inadvertently interchange two different concepts. The purpose of this study was to evaluate to what extent the frailty phenotype may be explained by the index. METHODS: Cross-sectional analysis including 393 participants with HIV aged 50 or older. Somers' delta (d) was calculated and a multinomial logistic regression model was run to determine to what extent the VACS index scores explained the probability of being pre-frail or frail. RESULTS: Mean age 57.6 (SD 6.5) years, and 87.3% men. A weak, but positive association between the VACS 2.0 index score and the frailty phenotype was established (Somers' d= .120, P< .001). The multinomial logistic regression showed that pre-frail and frail participants had higher probabilities for greater VACS index scores (OR= 1.05, 95% CI 1.01-1.09; P=.006 and OR= 1.17, 95% CI 1.09-1.26; P < .001, respectively); however, VACS index only explained < 12% of the variability observed in the frailty phenotype. CONCLUSIONS: High VACS index scores were associated with a greater probability of being frail; however, with a weak association. Thus, we should be cautious when using the VACS index as a general proxy of frailty, particularly for the frailty phenotype. However, the VACS Index may be used as a means to identify persons who might benefit from further comprehensive geriatric assessment.< Leer menos