This study aims to analyze the applicability of a simplified question in assessing diet quality of adolescents in a cross-sectional school-based study carried out in a sample of high school students. Diet quality self-perception was obtained when the participant was inquired about own diet considering "excellent", "good", "fair" or "poor" responses. We evaluated meals habits and food intake through food frequency questionnaire. The revised version of the Brazilian Healthy Eating Index (BHEI-R) was estimated and we identified three dietary patterns using factor analysis. "Good" self-perceived diet quality was reported by 56% of adolescents and was associated with regular consumption of fruits and vegetables, meal profile and high healthy eating index scores. However, consumption of foods harmful to health was not perceived as characteristic that affects diet quality. The evaluated question showed sensitivity of 28% to detect good quality diets and specificity of 79% to identify low nutritional value diets. The use of a simplified question to assess dietary habits of adolescents is limited, since the consumption of high-fat, high-sugar and high-sodium food was not recognized as an indicator of low quality diet.