Purpose As people around the world are facing the Covid-19 outbreak, their perception of oral health problems could be changed. This study aimed to evaluate the immediate effects of the Covid-19 pandemic on oral health-related quality of life (OHRQoL) of adolescents. Methods A cohort study with schoolchildren from southern Brazil was conducted. Data on adolescents' OHRQoL were collected from December 2019 to February 2020 (T1), before the Brazilian Covid-19 outbreak. Posteriorly, the data were collected again in June and July of 2020 (T2), under the Brazilian Covid-19 outbreak. The OHRQoL was assessed using the Brazilian short version of the CPQ11-14. Demographic and socioeconomic characteristics and the degree of social distancing were also assessed. Changes in OHRQoL between T1 and T2 were evaluated by adjusted Multilevel Poisson regression models for repeated measures. Results From 290 individuals evaluated at T1, 207 were reevaluated at T2 (response rate of 71.3%). The overall CPQ11-14 mean score was significantly lower during the pandemic, reducing from 10.8 at T1 to 7.7 at T2. This significant reduction was also observed for all CPQ domains, indicating a lower negative impact of oral conditions on adolescents' quality of life during the pandemic. Adolescents from families that had a middle or low degree of social distancing during the pandemic and whose parents were harmed in employment had higher CPQ11-14 scores. Conclusion Overall and specific-domains CPQ-14 scores were significantly lower during the Brazilian Covid-19 outbreak, indicating a decrease in the perception of oral health problems by adolescents over that period.