IMPORTANCE: In primary care settings, generalized anxiety disorder (GAD) and panic disorder are common but underrecognized illnesses. Identifying accurate and feasible screening instruments for GAD and panic disorder has the potential to improve detection and facilitate treatment. OBJECTIVE: To systematically review the accuracy of self-report screening instruments in diagnosing GAD and panic disorder in adults. DATA SOURCES: We searched MEDLINE, PsycINFO, and the Cochrane Library for relevant articles published from 1980 through April 2014. STUDY SELECTION: Prospective studies of diagnostic accuracy that compared a self-report screening instrument for GAD or panic disorder with the diagnosis made by a trained clinician using Diagnostic and Statistical Manual of Mental Disorders or International Classification of Diseases criteria. RESULTS: We screened 3605 titles, excluded 3529, and performed a more detailed review of 76 articles. We identified 9 screening instruments based on 13 articles from 10 unique studies for the detection of GAD and panic disorder in primary care patients Across all studies, diagnostic interviews determined that 257 of 2785 patients assessed had a diagnosis of GAD while 224 of 2637 patients assessed had a diagnosis of panic disorder. The best-performing test for GAD was the Generalized Anxiety Disorder Scale 7 Item (GAD-7), with a positive likelihood ratio of 5.1 (95% CI, 4.3-6.0) and a negative likelihood ratio of 0.13 (95% CI, 0.07-0.25). The best-performing test for panic disorder was the Patient Health Questionnaire, with a positive likelihood ratio of 78 (95% CI, 29-210) and a negative likelihood ratio of 0.20 (95% CI, 0.11-0.37). CONCLUSIONS AND RELEVANCE: Two screening instruments, the GAD-7 for GAD and the Patient Health Questionnaire for panic disorder, have good performance characteristics and are feasible for use in primary care. However, further validation of these instruments is needed because neither instrument was replicated in more than 1 primary care population.