A systematic method for clinical description and classification of both normal and abnormal personality variants is proposed based on a general biosocial theory of personality. Three dimensions of personality are defined in terms of the basic stimulus-response characteristics of novelty seeking, harm avoidance, and reward dependence. The possible underlying genetic and neuroanatomical bases of observed variation in these dimensions are reviewed and considered in relation to adaptive responses to environmental challenge. The functional interaction of these dimensions leads to integrated patterns of differential response to novelty, punishment, and reward. The possible tridimensional combinations of extreme (high or low) variants on these basic stimulus-response characteristics correspond closely to traditional descriptions of personality disorders. This reconciles dimensional and categorical approaches to personality description. It also implies that the underlying structure of normal adaptive traits is the same as that of maladaptive personality traits, except for schizotypal and paranoid disorders.