Evidence from developmental psychology suggests that representing the contents of other people's thoughts and beliefs depends on a component of reasoning about other minds (theory of mind) that is distinct from the earlier-developing mental-state concepts for goals, perceptions, and feelings. To provide converging evidence, the current study investigated the substrate of the late-developing process in adult brains. Three regions--the right and left temporo-parietal junction and the posterior cingulate--responded selectively when subjects read about a protagonist's thoughts, but not when they read about other subjective, internal states or other socially relevant information about a person. By contrast, the medial prefrontal cortex responded equivalently in all of these story conditions, a result consistent with a broader role for medial prefrontal cortex in general social cognition. These data support the hypothesis that the early- and late-developing components of theory of mind rely on separate psychological and neural mechanisms, and that these mechanisms remain distinct into adulthood.