Purpose: We assessed the feasibility of the ethyl glucuronide biomarker (EtG) through nail sampling to measure alcohol use among youth living with HIV in the United States (YLWH, N = 183); we also evaluated concordance between this EtG biomarker and self-reported measures of alcohol use, specifically, the Alcohol Timeline Followback (TFLB) and Alcohol, Smoking, and Substance Involvement Screening Test (ASSIST). Methods: EtG, TFLB, and ASSIST were collected at 4 points over 1 year. At baseline and 52 weeks, 78.1% and 70.1%, respectively, provided a valid (full or partial) sample. Results: At 16 weeks, EtG was associated with ASSIST (r = .25, p < .05). At 28 weeks and 52 weeks, TFLB and ASSIST were correlated with EtG (at 28 weeks r = .23, p < .05 and r = .41, p < .01, respectively; at 52 weeks r = .34, p < .01 and r = .25, p < .05, respectively). Conclusions: We found that nail-based EtG biomarker was feasible to measure alcohol use among YLWH; we also found concordance between EtG, TLFB, and ASSIST, supporting ongoing use of self-reported alcohol use measures with YLWH.