Elevated psychological distress and concomitant dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has been implicated as one pathway that links the stress of caregiving with adverse health outcomes. This study assessed whether perceived social support might mitigate the psychological, endocrine and health consequences of caregiver stress in parents of children with autism and attention deficit hyperactivity disorder (ADHD). Parental caregivers completed measures of psychological distress, perceived availability of social support and physical health complaints. To capture important parameters of the basal diurnal cortisol pattern, caregivers collected salivary cortisol at waking, 30 min post waking, 1200 h and 2200 h on two consecutive weekdays. Psychological distress and self reported physical health complaints were inversely related to scores on all support subscales: tangible, belonging, self esteem and appraisal. Results further revealed a significant, positive association between magnitude of the cortisol awakening response (CAR) and caregivers' self esteem. As a buffer between the stress of caregiving and adverse physical health outcomes, social support acts to reduce stress appraisals and mitigate disturbances of the HPA axis. Moving forward, intervention programmes might seek to increase caregivers' perceived availability of social resources. (Contains 3 tables.)