objective: the objective of the present study is to analyze the effect of stress on sleep quality in a group of adolescents. method: two high schools in alfenas, southern minas gerais state, brazil, were chosen to participate in the study. the sample consisted of both genders (n=160) with 65.63% females. the age range of participants was 15 to18 years. the pittsburgh sleep quality index (psqi) was applied for collection of data to quantify sleep quality. the lipp inventory of stress symptoms that objectively identifies symptoms of stress was applied. results: it was observed that 23.53% of stressed students and 45.33% of unstressed ones sleep well; 76.47% of stressed pupils and 54.67% of those unstressed do not sleep well. with regard to school performance, a mean of 0.65 was found for stressed students and 0.60 for those without stress, mann-whitney (p=0.0596). conclusion: stress contributed to raising the percentage of poor sleepers, as ell as increasing ean school performance.