AbstractThere has been significant disruption to the lives and mental health of adolescents during the COVID-19 pandemic. The purpose of this study was to assess the psychological and lifestyle impact of the pandemic on Australian adolescents, using an online survey, administered during the outbreak. Self-report surveys were administered online to a sample of 760 Australian adolescents aged 12–18 years assessing impact on a range of domains including behaviour, education, relationships, lifestyle factors (exercise, technology use, and sleep), and mental health outcomes (psychological distress, loneliness, health anxiety and well-being). Results showed that three quarters of the sample experienced a worsening in mental health, since the pandemic began, with negative impacts reported on learning, friendships and family relationships. There were also high higher levels of sleep disturbance, psychological distress and health anxiety, relative to normative samples. Effects on mental health were worse among those who reported a previous diagnosis of depression and/or anxiety relative to those without no such history. Adolescents are already vulnerable to the onset of mental illness at this developmental stage, and the current research underscores the need to find rapid and accessible ways to support adolescent mental health during times of crisis.