This article attempts to illustrate the importance of a developmental perspective in child health psychology. Research is reviewed relating motor, cognitive, and psychosocial development to exposure to health hazards, to an understanding of behavior-health relationships, to the assumption of personal responsibility for health, and to behavioral and emotional responses to illness and injury. In presenting this model of integration between developmental and health psychology, we propose that a developmental perspective be added as a fourth dimension to the commonly employed three-dimensional conceptualization of health psychology.