This review aims to clarify which instruments measuring at-risk and problem gambling (ARPG) among youth are reliable and valid in light of reported estimates of internal consistency, classification accuracy, and psychometric properties. A systematic search was conducted in PubMed, Medline, and PsycInfo covering the years 2009–2015. In total, 50 original research articles fulfilled the inclusion criteria: target age under 29 years, using an instrument designed for youth, and reporting a reliability estimate. Articles were evaluated with the revised Quality Assessment of Diagnostic Accuracy Studies tool. Reliability estimates were reported for five ARPG instruments. Most studies (66%) evaluated the South Oaks Gambling Screen Revised for Adolescents. The Gambling Addictive Behavior Scale for Adolescents was the only novel instrument. In general, the evaluation of instrument reliability was superficial. Despite its rare use, the Canadian Adolescent Gambling Inventory (CAGI) had a strong theoretical and methodological base. The Gambling Addictive Behavior Scale for Adolescents and the CAGI were the only instruments originally developed for youth. All studies, except the CAGI study, were population based. ARPG instruments for youth have not been rigorously evaluated yet. Further research is needed especially concerning instruments designed for clinical use.