Importance: Canada, Uruguay, and 18 states in the United States (US) have legalized use of nonmedical (recreational) cannabis for adults, yet the impact of legalization on adolescent cannabis use remains unclear. Objective: This study examined whether cannabis legalization for adults predicted changes in the probability of cannabis use among adolescents ages 13-18 years. Design: Data were drawn from 3 prospective, longitudinal studies of youth centered in 3 US states: Oregon, New York, and Washington, respectively. Data were collected either annually or biannually depending on the study between 1999 and 2020. During this time, Oregon (2015) and Washington (2012) passed cannabis legalization; New York did not. Multilevel modeling of repeated measures tested whether legalization predicted within- or between-person change in cannabis use over time. Items were harmonized and pooled across studies for analysis. Setting: Participants in each study were offspring of participants in earlier longitudinal studies using school-based samples. Participants: In each study, youth averaged 15 years of age (total N = 940 youth); between 49% and 56% of respondents were female, and between 11% and 81% were Black/African American and/or Latinx. Main Outcomes and Measures: Respondents self-reported their past-year cannabis use (1 yes, 0 no) at each assessment. Legalization was coded as both time-varying (1 legal, 0 not legal at each assessment) and time-fixed (proportion of years living under legalization). Results: Change in legalization status across adolescence was not significantly related to within-person change in the probability of cannabis use (b(se) = .15(.21), p = .492). Youth who spent more of their adolescence under legalization were no more or less likely to have used cannabis at age 15 years than adolescents who spent little or no time under legalization (between-person; b(se) = .34(.19), p = .073). Conclusions and Relevance: The current study addresses several limitations of repeated cross-sectional studies of the impact of cannabis legalization on adolescent cannabis use. Findings are not consistent with changes in the prevalence of adolescent cannabis use following legalization. Ongoing surveillance and analyses of subpopulations are recommended.