PURPOSEEmotional symptoms impose a significant burden on children and adolescents, particularly in low- and middle-income countries, where treatment options are limited. Addressing this gap, we developed and assessed a brief cognitive-behavioral internet-delivered intervention targeting anxiety and depression symptoms in Brazilian youth.METHODSWe conducted a single-blind, two-arm, parallel-group, randomized controlled trial in youth aged 8-17 with a total T-score ≥70 on the 25-item version of the Revised Children's Anxiety and Depression Scale, parent (RCADS-P) and child report (RCADS-C). Participants were randomly assigned (1:1) to cognitive-behavioral intervention (5 weekly sessions conducted by videoconference focused on skills training) or psychoeducation. Sessions were conducted with youth and their caregivers jointly. Participants were assessed at baseline, at post-treatment and at the 30-day follow-up. The primary outcome was the change from baseline to post-treatment on RCADS-P and RCADS-C scores. This trial is registered with ClinicalTrials.gov, NCT05139433.RESULTSBetween October 15, 2021, and February 27, 2023, 280 participants were randomized, with 231 completing post-treatment and 214 completing follow-up assessments. In comparison to participants in the psychoeducation group, participants in the intervention group showed greater reductions in emotional symptoms according to youths (mean difference = 4.3, p = .013, standardized mean difference (SMD) = 0.25 [95% confidence interval (CI) 0.05-0.44]) and parents (mean difference = 3.6, p = .023, SMD = .21 [95% CI 0.03-0.40]), as well as in anxiety scores according to youths (mean difference = 4.4, p = .0043, SMD = 0.28 [95% CI 0.09-0.47]) and parents (mean difference = 3.2, p = .030, SMD = 0.21 [95% CI 0.02-0.40]). There were no significant differences in depression scores at post-treatment according to youth (mean difference = 2.9, p = .063, SMD = 0.19 [95% CI -0.01 to 0.39]) or parents (mean difference = 2.2, p = .15, SMD = 0.15 [95% CI -0.05 to 0.33]), but effects emerged at the 30-day follow-up. No serious adverse events were reported.DISCUSSIONThe cognitive-behavioral intervention was effective in reducing emotional symptoms in children and adolescents in Brazil. This intervention holds promise for enhancing access to mental health care within a stepped-care model in public health contexts.