Purpose: The recent legalization of nonmedical marijuana use in several U.S. states has unknown implications for those who are actively parenting. This study examined parents' reactions to marijuana legalization and changes in attitudes and behaviors over time. Methods: Data were from a gender-balanced, ethnically diverse sample of 395 parents in Washington State who were participating in the longitudinal Seattle Social Development Project. Participants were interviewed 15 times between 1985 (age 10) and 2014 (age 39). Adult nonmedical marijuana use was legalized in Washington in 2012 and retail outlets opened in 2014. Results: Results showed (1) one third of parents incorrectly believed the legal age of nonmedical marijuana use to be 18; (2) significant increase in approval of adult marijuana use and decrease in perceived harm of regular use; (3) wide opposition to teen use and use around one's children; and (4) substantial increases in frequency of use and marijuana use disorder among parents who used. Conclusions: Despite increased acceptance and frequency of adult use, parents remain widely opposed to teen use but need facts and strategies for talking with their children about marijuana.