Little is known about the implications of cannabis legalization on adolescent health behaviors. This study sought to examine the relationship between recreational cannabis legalization and adolescent sexual risk behaviors. Data on 371,487 respondents who have ever had sexual intercourse from 41 states in the 2005 to 2019 Youth Risk Behavior Survey was linked with data on state-level cannabis policies. Difference-in-differences logistic regression models were conducted. Recreational cannabis legalization was associated with a reduced likelihood of respondents having 2+ sexual partners (adjusted OR [aOR] 0.63, 95% CI [0.47, 0.84]), but had no association with condom use (aOR 0.94, 95% CI [0.80, 1.11]). Changing social norms around cannabis is a potential pathway linking cannabis legalization to a reduction in sexual risk behaviors.