ImportanceAnxiety in children and adolescents is associated with impaired functioning, educational underachievement, and future mental health conditions.ObjectiveTo review the evidence on screening for anxiety in children and adolescents to inform the US Preventive Services Task Force.Data SourcesPubMed, Cochrane Library, PsycINFO, CINAHL, and trial registries through July 19, 2021; references, experts, and surveillance through June 1, 2022.Study SelectionEnglish-language, randomized clinical trials (RCTs) of screening; diagnostic test accuracy studies; RCTs of cognitive behavioral therapy (CBT) or US Food and Drug Administration–approved pharmacotherapy; RCTs, observational studies, and systematic reviews reporting harms.Data Extraction and SynthesisTwo reviewers assessed titles/abstracts, full-text articles, and study quality and extracted data; when at least 3 similar studies were available, meta-analyses were conducted.Main Outcomes and MeasuresTest accuracy, symptoms, response, remission, loss of diagnosis, all-cause mortality, functioning, suicide-related symptoms or events, adverse events.ResultsThirty-nine studies (N = 6065) were included. No study reported on the direct benefits or harms of screening on health outcomes. Ten studies (n = 3260) reported the sensitivity of screening instruments, ranging from 0.34 to 1.00, with specificity ranging from 0.47 to 0.99. Twenty-nine RCTs (n = 2805) reported on treatment: 22 on CBT, 6 on pharmacotherapy, and 1 on CBT, sertraline, and CBT plus sertraline. CBT was associated with gains on several pooled measures of symptom improvement (magnitude of change varied by outcome measure), response (pooled relative risk [RR], 1.89 [95% CI, 1.17 to 3.05]; n = 606; 6 studies), remission (RR, 2.68 [95% CI, 1.48 to 4.88]; n = 321; 4 studies), and loss of diagnosis (RR range, 3.02-3.09) when compared with usual care or wait-list controls. The evidence on functioning for CBT was mixed. Pharmacotherapy, when compared with placebo, was associated with gains on 2 pooled measures of symptom improvement—mean difference (Pediatric Anxiety Rating Scale mean difference, −4.0 [95% CI, −5.5 to −2.5]; n = 726; 5 studies; and Clinical Global Impression–Severity scale mean difference, −0.84 [95% CI, −1.13 to −0.55]; n = 550; 4 studies) and response (RR, 2.11 [95% CI, 1.58 to 2.98]; n = 370; 5 studies)—but was mixed on measures of functioning. Eleven RCTs (n = 1293) reported harms of anxiety treatments. Suicide-related harms were rare, and the differences were not statistically significantly different.Conclusions and RelevanceIndirect evidence suggested that some screening instruments were reasonably accurate. CBT and pharmacotherapy were associated with benefits; no statistically significant association with harms was reported.