Research that has assessed the psychophysiological consequences of caregiver stress in young and middle aged caregivers, that is, in populations not contending with age associated decline of the endocrine and immune systems, has been scarce and yielded inconsistent findings. To extend work in this area, this study assessed the psychosocial, endocrine and immune consequences of caregiver stress in a cross sectional sample of young and middle aged caregivers of children with autism and attention deficit hyperactivity disorder (ADHD) compared against parents of typically developing children. Caregivers (n = 56) and parent controls (n = 22) completed measures of psychological distress (perceived stress, anxiety / depression), social support and physical health complaints. To capture important indices of the diurnal cortisol pattern, cortisol was measured at waking, 30 minutes post waking, 1200h and 2200h on two consecutive weekdays. Venous blood was taken to assess systemic concentrations of proinflammatory biomarkers, interleukin-6 (IL-6) and C-reactive protein (CRP). Caregivers scored markedly higher on all measures of psychological distress; scores on social support subscales, however, were significantly lower in this group. Diurnal patterns of cortisol secretion did not differentiate between the groups; however, caregivers displayed elevated systemic concentrations of the proinflammatory biomarker, CRP and reported more frequent episodes of physical ill health. The stress of caregiving exacts a significant psychophysiological toll, that is, even in the absence of HPA dysregulation, caregivers demonstrated elevated concentrations of proinflammatory biomarkers and, therefore, might be at greater risk for diseases fostered by disinhibition of the inflammatory response.