The presence of diabetes mellitus and hypertension was associated with lower physical component summary scores. However, there was no association of PCS with awareness, or treatment for these conditions. In contrast, mental component summary scores were lower in those who were aware of the diagnosis of diabetes mellitus or hypertension than in those who were unaware of their AZ 960 disease status. However, this was partly because those who had diabetes mellitus or hypertension but were unaware of it had higher MCS than those without disease while those who were aware of the disease had slightly lower MCS. This finding, of higher MCS in those with undiagnosed disease, has not been replicated in other populations. Furthermore, our previous study did not comprehensively assess all the complications associated with these disorders to allow adjustment for these complications. As such, the presence of comorbid conditions, by making the diagnosis or treatment of these diseases more likely, may confound the association between awareness or treatment for these disorders and HRQoL. In addition, treatment for hypertension appears to negatively affect HRQoL among those diagnosed with hypertension. We therefore aimed to determine the contributions of disease awareness, treatment and comorbid conditions on HRQoL in chronic disease by using data from a health survey in which individuals were classified as having disease based on history and objective indicators along with detailed assessment of comorbid conditions. We focussed on three common chronic medical conditions, namely diabetes, hypertension and dyslipidemia. Our findings with respect to medications in hypertension are in contrast to findings published earlier where individuals taking medication had worse HRQoL scores, both PCS and MCS, compared to those not receiving medication. It is possible that these differences are due to differences in the type of antihypertensive agents prescribed and in use by subjects in that study and ours. Indeed, it has been shown that drugs belonging to the same class of agents with similar clinical profiles have vastly different effects on health related quality of life. Also, individuals not taking medication included both those with diagnosed disease as well as those with undiagnosed disease, and comorbid conditions were not adjusted for in that study. Secondly, we report varying effects of medications in different diseases on MCS. The reasons for this are not clear, and need to be explored further. One possibility is the occurrence of adverse effects with lipidlowering therapy which affect mental well-being. Indeed, newer studies on cholesterol lowering drugs report more adverse effects and effects on HRQoL, while older studies have reported no reductions in HRQoL due to therapy. Like with antihypertensive drugs, it is likely that these differences are also due to differing quality of life effects of the various drugs available and prescribed for dyslipidemia.