IntroductionWhile the study of conspiracy theory beliefs is a relatively new research area, there has been a rise in academic interest in recent years. The literature provides evidence of relationships between conspiracy theory beliefs and a range of factors, but the vast majority of studies are limited to adult samples, and it is unclear how such beliefs present in adolescence.MethodsThe systematic review was conducted according to the PRISMA‐S format. Relevant databases were searched up to February 23, 2023, for quantitative studies related to adolescent conspiracy theory beliefs.ResultsThe six included articles show that conspiracy theory beliefs are present from the start of adolescence, and stable from age 14 upwards, with correlations reported for mistrust and paranoid thinking. Negative relationships were reported for cognitive factors such as ontological confusion, cognitive ability, and actively open‐minded thinking. Health‐related beliefs correlated with adverse childhood experiences, peer problems, conduct, and sociodemographic factors. Right‐wing authoritarianism and anxiety positively correlated with intergroup conspiracy theory beliefs.ConclusionWhile some factors from adult studies are replicated in the review, there are differences between age groups. The age at which conspiracy theory beliefs begin to form indicate developmental aspects of adolescence, and possibly childhood, that require further examination. Cognitive factors show promise for interventions and should be explored further. However, the lack of studies using adolescent populations is an issue that must be resolved for a greater understanding of conspiracy theory beliefs and a move toward effective interventions.