An important public concern about the impact of recreational cannabis legalization is how it may affect adolescent cannabis use. Prior research on this issue has primarily focused on the implications of "medical" cannabis legalization for adolescents and used data that cover a relatively short post-legalization period. This study extends this line of research by examining the relationship between "recreational" cannabis legalization and adolescent cannabis use in Washington State, using the National Survey of Drug Use and Health (NSDHU) data from 2005 to 2019. Based on a quasi-experimental research design, this study found some evidence suggesting a positive effect of recreational legalization on the prevalence of adolescent cannabis use and cannabis initiation. Findings suggest the need to create a cannabis regulatory environment that minimizes adolescent access to this drug.