There is evidence to suggest that a decline in physical functioning with advancing age is independent of mental health, which appears to remain relatively stable. There is additional evidence to suggest that those with a chronic disease also experience a decline in physical function while the mental health remains relatively stable. Using a cross-sectional design, data from the US population norms for the Medical Outcomes Study SF-36 are examined and compared to SF-36 data collected for four patient groups. Patient groups include kidney dialysis patients, multiple sclerosis patients, kidney transplant patients and patients with severe osteoarthritis of the hip prior to total hip replacement. Overall scores and scores within 10-year age groupings are examined in order to compare the physical functioning and mental health scores of the general population with those of the four patient groups. Results support the hypothesis that physical functioning declines with advancing age and with the development of chronic disease, but mental health remains remarkably stable regardless of chronic disease and/or advancing age. This observation suggests a process of psychological adjustment or adaptation to the physical difficulties encountered with advanced age or disability, and implies that this adjustment process may in fact be quite strong.