We review the attributes of inhibited and uninhibited infant temperaments, and their developmental trajectories into early adulthood. Inborn individual differences in infants' propensity to respond to novel people and objects are associated with persistent differences in the responsivity of the amygdala to novelty, as measured with functional magnetic resonance imaging, after more than 20 years of development. Because an inhibited temperament is a risk factor for developing later psychiatric disorders, particularly generalized social anxiety disorder, temperamental differences are confounds in neuroimaging and genetic studies. Longitudinal studies are a unique tool for understanding the developmental and temperamental risk factors for psychiatric disorder.