Introduction:
Many countries have closed schools in order to prevent the spread of COVID-19. As a result, adolescents have become socially isolated.

Aim:
The aim of this cross-sectional study was to determine the psychosocial effects of the COVID-19 pandemic on students attending a private high school in Istanbul, Turkey.

Material and methods:
Participants completed an online questionnaire including the COVID-19 phobia scale (C19P-S), trait anxiety inventory (TAI), and questions about their sociodemographic characteristics, COVID-19 prevention measures taken, and pandemic-related life changes. The minimum sample number was calculated as 199 students, and 92% (n = 183) of this target was achieved.

Results and discussion:
The most common changes in their lives during the pandemic were increased use of digital devices, feeling socially isolated, and lethargy and laziness due to staying at home for a prolonged period. Based on the group medians, 39 (21.3%) of all participants were found to have COVID-19 phobia, with phobia in the psychological, somatic, social, and economic domains in 74 (40.4%), 57 (31.1%), 66 (36.1%), and 47 (25.7%) of participants, respectively. Based on the median TAI score, 55 (30.1%) of the participants had anxiety.

Conclusions:
Adolescents are a vulnerable group; to protect their mental health during the pandemic, risks must be reduced and preventive mental health interventions increased. Parents should provide guidance to adolescents in order to provide access to sources of accurate information, use the internet to support individual and social development, and create alternative ways for peer interaction to reduce isolation and loneliness.