Background: Four-day school week (FDSW) use has increased substantially among US districts in recent years, but limited data exist on health impacts of this school schedule. This study examined associations of reduced school exposure via FDSWs with adolescent health and risk behaviors, obesity, and food security. Methods: Self-report data from 8th- and 11th-grade students from the Oregon Healthy Teens survey across 5 survey years (odd years 2007-2015, total N = 91,860-104,108 respondents depending on the survey question) were linked to a FDSW indicator. Regression analyses controlling for student and school characteristics compared outcomes between students in 4- and 5-day schools overall (without school fixed effects) and outcomes associated with switching to a FDSW (with school fixed effects). Results: When controlling for multiple student- and school-level factors, we observed adolescents in FDSW schools report they consume sugar sweetened beverages more frequently and water less frequently, have access to fewer days of physical education, are more likely to be food insecure, and are more likely to report the use of any drugs and specifically marijuana than 5-day school week students. Conclusions: Limiting exposure to the school environment via FDSWs may impact adolescent health behaviors, including diet, physical activity, and drug use.