BACKGROUND AND OBJECTIVES: Adolescent substance use is associated with numerous adverse health outcomes. A hospitalization represents an opportunity to identify and address substance use. We sought to describe self-reported and documented substance use among hospitalized adolescents. METHODS: We conducted a cross-sectional survey of adolescents aged 14 to 18 years old admitted to two pediatric hospitals between August 2019 and March 2020. Using previously validated questions, we assessed the proportion of adolescents reporting ever, monthly, and weekly use of alcohol, marijuana, tobacco, electronic cigarettes, and other illicit drugs and nonmedical use of prescription medications. We reviewed medical records for substance use documentation. RESULTS: Among 306 respondents, 57% were older (16-18 years old), 53% were female, and 55% were of non-Hispanic white race and ethnicity. The most frequently reported substances ever used were alcohol (39%), marijuana (33%), and electronic cigarettes (31%); 104 (34%) respondents reported ever use of.1 substance. Compared with younger adolescents, those aged 16 to 18 years were more likely to report ever use of alcohol (29% vs 46%; P =.002), marijuana (22% vs 41%; P,.001), and $2 drugs (26% vs 40%; P =.009). A positive substance use history was rarely documented (11% of records reviewed), and concordance between documented and self-reported substance use was also rare. CONCLUSIONS: In this study of hospitalized adolescents, the most commonly reported substances used were alcohol, marijuana, and electronic cigarettes. Positive substance use documentation was rare and often discordant with self-reported substance use. Efforts to improve systematic screening for substance use and interventions for prevention and cessation in hospitalized adolescents are critically needed.