Diabetes Mellitus is an illness that affects more than 100,000 people in New Zealand. This study examined the variables which were thought to be most likely to impact on the quality of life of people with either Insulin Dependent Diabetes Mellitus (IDDM) or Non-Insulin Dependent Diabetes Mellitus (NIDDM). Diabetes requires a high degree of self-management on a daily basis. The challenges for people with diabetes are to maintain a healthy level of blood glucose by carrying out adequate self-care behaviours. It was thought these may represent barriers to unrestricted quality of life, and the study investigated the degree to which cognitive-affective processes were diverted into self-care and illness appraisal. The two groups were studied to investigate which psychological factors would influence perceptions of wellbeing, and whether or not the psychological areas of significance were correlated with blood glucose levels (HbA1C), depicting good metabolic control. Using a questionnaire survey method, this study examined the psychological processes of 99 people with diabetes (36 IDDMs and 63 NIDDMs), assessing in particular, their self-efficacy, perception of risk, and psychological control, all considered to be factors that would be likely to affect their quality of life. Measures used included illness appraisal, wellbeing and self-efficacy scales, as well as a small qualitative section eliciting personal comments. The findings indicated a moderate level of self-efficacy and wellbeing across the sample which was adversely affected when they were compelled to take barriers to effective self-care into account. Risk perception was considered to be inadequate, especially when correlated with other factors, suggesting that self-efficacy was maintained by sidelining the risks or threats of diabetes. On the whole, the sample were particularly effective at maintaining adequate weight through diet, and a significant proportion were not taking any medication at all. Severe hypoglycaemic episodes were rare. Perception of control was another issue which appeared to be adequate for the sample, but it was found that people's perceived control was a more cogent variable than actual metabolic control (as measured by HbA1C assay). It was possible to infer stages of self-efficacy according to the manner in which people responded. Drawing on self-efficacy measures found to be effective in assessing populations with chronic conditions, it was found that there was some support for the notion that resistance self-efficacy and coping self-efficacy were the mechanisms at work for these people. Comments from respondents showed a desire for more information and better public awareness of diabetes, and offered some insight into the mechanisms by which people maintain an adequate quality of life despite chronic illness.