Objective: To assess the sleep quality of Brazilian adolescents during the COVID-19 pandemic. Methods: Observational, analytical, cross-sectional study with data from a questionnaire on individual characteristics and health, Epworth Sleepiness Scale and the Pittsburgh Sleep Quality Index (PSQI). 153 adolescents participated -61.4% females, 38.6% males, aged 13 to 18 years, enrolled at school. Results: 58.2% worsened their sleep quality during the pandemic. In the PSQI, 22 (14.4%) had a good, 104 (68%), a poor sleep quality, 27 (17.6%), suggestive of sleep disorders. Excessive daytime sleepiness occurred in 44.4% of the students. Significant associations appeared between sleep and decreased school motivation (p = 0.005), and between sleep and sex (p = 0.015). The pandemic affected more the females -25.5% reported worse sleep quality, 67% had PSQI scores suggestive of sleep disorders; 46 (30.1%) students reported stress, anxiety, sadness -76.1% were girls. Discussion: Adolescents had impaired sleep during the COVID-19 pandemic, reinforcing their sleep must be assessed in critical periods.