Introduction
Psychiatric symptoms are prevalent among teenagers and consistently associated with impaired academic performance.

Objective
This study aimed to examine the relationship between symptoms of depression, anxiety, and stress and academic performance among high school students in southern Brazil.

Methods
This cross-sectional study (2022) involved students from the Federal Institute of Rio Grande do Sul (IFRS), Brazil. Mental health was assessed using the Depression, Anxiety, and Stress Scale (DASS-21), and academic performance was estimated based on the average grades taken in the academic year. Data were analyzed using STATA 15.1 with Poisson regression for prevalence ratios. Results: Among 480 eligible students, 391 had complete data (response rate: 81.5%). The mean age was 17.0 years (SD = 1.5); 56% were male, 46% first-year students, 33% physically inactive, 5% smokers, 36% reported alcohol consumption, and 32% had good or very good sleep quality. The mean DASS-21 score was 15.2 (95%CI 14.4–16.5). Severe or very severe symptoms were observed in 16.2% for depression, 15.3% for anxiety, and 9.1% for stress, with 22.3% presenting at least one severe outcome. The mean academic grade was 7.8 (SD = 1.4); 21% scored <7.0 and 17% ≥9.0. Higher mental health scores were associated with lower and reduced higher academic performance. Depression and stress, but not anxiety, were associated with poorer performance; only depression showed an inverse association with high performance.

Conclusion
This study demonstrated a negative association between depressive and stress symptoms and academic performance in high school students, while anxiety symptoms were not significantly associated.