What effect the outbreak of the COVID-19 pandemic has had on adolescents' psychosocial functioning is currently unknown. Using the data of 1767 (50.2% female and 49.8 male) adolescents in Sweden, we discuss adolescents' thoughts and behaviors around the COVID-19 outbreak, as well as reported changes in substance use, everyday life, relations, victimization, and mental health during the outbreak. Results showed that (a) the majority of adolescents have been complying with regulations from the government; (b) although most adolescents did not report changes in their psychosocial functioning, a critical number reported more substance use, conflict with parents, less time spent with peers, and poorer control over their everyday life; and (c) the majority of adolescents have experienced less victimization, yet poorer mental health, during the COVID-19 outbreak. Adolescent girls and adolescents in distance schooling were likely to report negative changes in their psychosocial functioning during the COVID-19 outbreak. Based on these findings, we suggest that society should pay close attention to changes in adolescents' psychosocial functioning during times of crisis.