Background: Alcohol contributes to numerous annual deaths and various societal problems not just in adult, but also in adolescent, populations. Therefore, it is vital to find methods for reliably detecting alcohol use for early preventative measures. Research has shown phosphatidylethanol (PEth) to be superior to self-report instruments and indirect biomarkers for alcohol consumption in adult populations. However, the transferability onto an adolescent population has not yet been investigated. Methods: N = 106 adolescents and young adults aged between 13 and 21 years were included. PEth analysis using high-pressure liquid chromatography-tandem mass spectrometry was performed on dried blood spot samples. Self-report questionnaires for alcohol consumption (Alcohol Use Disorders Identification Test-Consumption, AUDIT-C, and Timeline Followback, TLFB) and drug and alcohol consumption (Detection of Alcohol and Drug Problems in Adolescents, DEP-ADO) were completed by each participant. Results: AUDIT-C scores showed large correlations with PEth 16:0/18:1 (r s = 0.732) and PEth 16:0/18:2 (r s = 0.661) concentrations. AUDIT-C with a cutoff value ≥3 was largely correlated with PEth 16:0/18:1 (g = 0.411) and showed a medium-sized correlation with PEth 16:0/18:2 (g = 0.397) concentrations. Using an AUDIT-C cutoff value ≥5 showed large correlations with both PEth 16:0/ 18:1 (g = 0.510) and PEth 16:0/18:2 (g = 0.497) concentrations, respectively. ROC curves indicated higher PEth concentrations are a good model for detecting positive AUDIT-C cutoff values (AUROC range: 0.800 to 0.849). PEth concentrations showed medium to large correlations with DEP-ADO and TLFB subscales (range r s = 0.469 to 0.746). Conclusion: The results suggest that PEth is a reliable and objective marker for quantifying alcohol consumption in adolescents and young adults. This could be of importance for early preventative measures against hazardous alcohol consumption, which is increasingly common at younger ages.