Schools around the world were closed during the spring 2020 lockdown to reduce the spread of COVID-19. As such, these rapid changes to adolescent daily routines may have had immediate as well as long-term effects on their physical, social, and mental health. Therefore, the aim of this study was to examine the experiences, health behaviors and perceived change in health behaviors among adolescents in Czechia during the spring 2020 lockdown. Adolescents (n = 3,440, 54% girls; M-age = 13.5 years, SD = 1.6) from all regions of Czechia were recruited to complete a self-report survey based on the Health Behaviour in School-aged Children study, with additional items on household disruptions and socialization during lockdown, as well as items on perceived changes in health behaviors during lockdown. First, we described the self-reported impacts of the spring lockdown by gender and grade. Second, log-linear analyses were used to examine the perceived behavioral changes based on standardized cut-off values reporting for health behaviors and gender. Less than a third, 19% and 32% of the respondents reported economic and psychosocial disruptions to their family life, 79% indicated they had positive opportunities for family interactions or learning new things. Girls and older adolescents reported the worst levels of social and mental well-being. Changes in respondents' perceived health behaviors varied by reported behavior frequencies and gender. These results may be useful to compare with future secular trends, and may serve as input in developing strategies to counter the impact of the spring 2020 or future similar lockdowns on the adolescents' well-being..