This thesis has three main research aims. First the development of a questionnaire to measure HRQOL of ICU patients. Second, to examine a model of HRQOL proposed to assist with the development of the questionnaire. Third, to examine the HRQOL outcomes of patient after hospital discharge. The proposed model is based on a review of conceptual issues related to Quality of Life (QOL), Health Status and HRQOL. After a content analysis of a broad range of definitions of QOL, Health Status and HRQOL, QOL was defined as a dynamic attitude, continually being modified by experience. It is a function of the cognitive and affective appraisals of the discrepancies between domain specific perceptions and expectations. HRQOL was defined as an individuals cognitive and affective response to, or the QOL associated with, their health status. Health status was seen to consist of two health dimensions, physical and psychological health, with each dimension being composed of a number of component measures assessed subjectively. The developed questionnaire, the Sydney Quality of Life (SQOL) had good construct validity, based on substantial correspondence between qualitative and quantitative data, and internal consistency data (factor analysis and Cronbach's alpha). It had good concurrent validity in relation to the Sickness Impact Profile. The second order factor analysis of the SQOL suggested that health status may consist of three dimensions, physical health, positive mental health and negative mental health. The HRQOL model when formally examined, using Structural Equation Modelling (using LISREL), was not supported. However, exploratory modelling supported the separation of mental health into positive and negative components. The structure of HRQOL was different for patients than for the community from which they came. Patients QOL was determined largely by positive mental and physical health, whereas community members QOL was largely determined by negative mental health. Sixty three percent of patients at 12 months after discharge had significantly worse physical and functional health, lower satisfaction with their lives, lower positive affect and poorer QOL. Overall, mental health adapts rapidly to the impact of serious physical ill health and hospitalisation. Implications for clinical practice are examined.