Study Objectives: The COVID-19 pandemic has challenged the population of affected areas in multiple dimensions. Adolescents have been especially affected with school closure and home confinement. The impact of the pandemic on sleep habits and quality of sleep and quality of life among adolescents has not been adequately characterized. We hypothesized that the COVID-19 pandemic has induced an evening shift of the daily rhythm among adolescents and adversely affected sleep quality and quality of life of high school students. Methods: Students were questioned about their usual bed and wake-up times and answered the Pittsburgh Sleep Quality Index Questionnaire, the Epworth Sleepiness Scale, the Horne-Osteberg Morningness-Eveningness Questionnaire, and the World Health Organization Quality of Life Questionnaire-abbreviated version before and during the pandemic. Results: Ninety-four students (64% females, aged 15 ± 1 years) participated in both phases of the study. Students delayed bed and wake-up times by 1.5 (0.5-2.0) and 2.0 (1.5-2.5) hours, respectively. Chronotype (per the Morningness-Eveningness Questionnaire) shifted toward eveningness during the pandemic. Sleep duration increased and quality of sleep (per the Pittsburgh Sleep Quality Index) improved only among those students with shorter sleep duration before the pandemic. During the pandemic, the physical and psychological domains of the World Health Organization Quality of Life Questionnaire worsened but the environmental domain improved as compared with the study before the pandemic. Conclusions: High school students have delayed bed and wake-up times and shifted chronotype toward eveningness during the COVID-19 pandemic. The worsening of the physical and psychological World Health Organization Quality of Life Questionnaire domains and improvement in the environmental domain highlight the conflicting experiences that high school students are facing during the COVID-19 pandemic.