To date, much of the research linking the stress of caring for children with developmental disabilities (e.g. Autism & Down syndrome) with parental health outcomes have tended to concentrate on mental health with less attention paid to the physical health consequences. Thus, this study sought to explore the psychosocial predictors of poor physical health in these caring parents. One hundred and sixty-seven parents (109 caregivers and 58 control parents) completed measures of stress, child problem behaviours, social support, mastery and physical health. Parents of children with developmental disabilities had poorer physical health compared to control parents. Stress and mastery, but not social support and problem behaviours, were significant predictors of poor physical health within caring parents for children with developmental disabilities. However, the association between mastery and physical health was mediated by perceived stress such that those parents who were higher on mastery reported less stress and better physical health; furthermore, the association between stress and physical health was moderated by social support; those parents high on social support and low in stress had better physical health. These results indicate that the paths between psychosocial factors and poor physical health in the caring parents are working synergistically rather than in isolation. They also underscore the importance of providing multi-component interventions that offer a variety of psychosocial resources to meet the precise needs of the parents.