Medical imaging technology has been used since the 1990s to make claims about how adolescent brains are different to adult brains. In turn these differences have been used to explain what are said to be typical patterns of adolescent behaviour like risk taking, sensation seeking and intense peer interaction. This article critically assesses the scientific basis of the claims that link observations about adolescent brains to adolescent behaviour via a critical review of the current literature. It argues that use of visual evidence to support claims about structural or functional differences from adolescent brains relies on naïve epistemic assumptions. It argues that there is currently no evidence to warrant claims that there are typical predictable differences in brain structure or function among adolescents or to suggest that adolescent behaviour is different from adult behaviour. The science of adolescent brains is testimony more to the continuing appeal of scientism and its promotion of biological reductionism than to careful and reflexive scientific practice.