Moral and legal notions engaged in clinical ethics should not only possess analytic clarity but a sound basis in empirical findings. The latter condition brings into question the expansion of the mature minor exception. The mature minor exception in the healthcare law of the United States has served to enable those under the legal age to consent to medical treatment. Although originally developed primarily for minors in emergency or quasi-emergency need for health care, it was expanded especially from the 1970s (...) in order to cover unemancipated minors older than 14 years. This expansion initially appeared plausible, given psychological data that showed the intellectual capacity of minors over 14 to recognize the causal connection between their choices and the consequences of their choices. However, subsequent psychological studies have shown that minors generally fail to have realistic affective and evaluative appreciations of the consequences of their decisions, because they tend to over-emphasize short-term benefits and underestimate long-term risks. Also, unlike most decisionmakers over 21, the decisions of minors are more often marked by the lack of adequate impulse control, all of which is reflected in the far higher involvement of adolescents in acts of violence, intentional injury, and serious automobile accidents. These effects are more evident in circumstances that elicit elevated affective responses. The advent of brain imaging has allowed the actual visualization of qualitative differences between how minors versus persons over the age of 21 generally assess risks and benefits and make decisions. In the case of most under the age of 21, subcortical systems fail adequately to be checked by the prefrontal systems that are involved in adult executive decisions. The neuroanatomical and psychological model developed by Casey, Jones, and Summerville offers an empirical insight into the qualitative differences in the neuroanatomical and neuropsychological bases of adolescent versus adult decision making. These and other data, as well as developing law bearing on the culpability of juvenile criminal offenders, argue for critically re-evaluating the expansion of the mature minor exception with regard to medical decision making, as well as in support of a rebuttable presumption in favor of treating minors as immature decisionmakers. The clinical ethics of adolescent medical decision making will need foundationally to be reconsidered. (shrink)