Prior to the COVID-19 pandemic, adolescents (N = 1,330; Mages = 15 and 16; 50% female), mothers, and fathers from nine countries (China, Colombia, Italy, Jordan, Kenya, Philippines, Sweden, Thailand, United States) reported on adolescents' internalizing and externalizing problems, adolescents completed a lab-based task to assess tendency for risk-taking, and adolescents reported on their well-being. During the pandemic, participants (Mage = 20) reported on changes in their internalizing, externalizing, and substance use compared to before the pandemic. Across countries, adolescents' internalizing problems pre-pandemic predicted increased internalizing during the pandemic, and poorer well-being pre-pandemic predicted increased externalizing and substance use during the pandemic. Other relations varied across countries, and some were moderated by confidence in the government's handling of the pandemic, gender, and parents' education.