The COVID-19 pandemic has shown varying effects on adolescents' mental health, psychosocial functioning, risk behaviours, and victimisation. This study aims to examine the changes reported by a sample of Swedish adolescents (N = 1607) at the end of the first year of the pandemic in relation to these factors. Data were collected with an electronic survey between September 2020 and February 2021, targeting upper-secondary high school students (aged 15-19 years). The results indicate a relatively low overall impact of the pandemic on Swedish upper-secondary school students, with notable gender differences. Compared to adolescent women, a higher percentage of adolescent men reported experiencing elevated levels of anxiety, depression, sleep disturbances, anger, and increased illicit drug use as consequences of the pandemic. In contrast, women demonstrated an increase in several salutogenic behaviours. Victimisation rates generally decreased during this period. These findings underscore the importance of heightened awareness among professionals within schools, social services, and healthcare settings regarding the distinct challenges encountered by a larger portion of adolescent men during the COVID-19 pandemic in Sweden.