This research investigates type 2 diabetes using a psychological approach grounded in self-regulatory theory. Diabetes mellitus is usually described as a long-term illness with serious physical consequences, and biomedical perspectives predominate in published diabetes research. Findings from the present study add to accumulating knowledge about diabetes by addressing an identifiable gap in the literature, namely, an understanding of the psychological processes involved in managing type 2 diabetes. The common sense model (CSM) of illness self-regulation was used as the conceptual framework for this study. The research sample (N = 1145) was identified from a medical database. A mailed questionnaire survey was used to obtain psychological and self-report data, and this was subsequently merged with clinical data from a review of the medical database. A response rate of 55% provided a total of 629 completed questionnaires. The age, gender, and cultural composition of the sample were a close match with those reported for the New Zealand type 2 diabetes population. Research findings contribute to self-regulatory theory by testing key relationships specified in the CSM. The identification of a relationship cluster connecting emotional illness responses with cyclical symptoms, serious consequences, strong illness identity, and low coherence, highlights an emotional pathway in diabetes self-regulation. Observed relationships support the interaction between cognition and affect proposed in the CSM. Results show significant relationships between treatment perceptions and diabetes self-management, and draw attention to the importance of family relationships in explaining diet and exercise patterns. Perceived consequences of diabetes play a pertinent role in explaining variance in quality of life, and diabetes-related distress. The CSM postulates coping responses mediate between representations and illness outcomes; current findings, showing that medication use mediates the relationship between treatment representations and HbA1c, support the predicted mediating relationship. It is concluded the common sense model provides a useful theoretical framework for research investigating self-care and wellbeing among people with type 2 diabetes. Potential implications for psychological theory and clinical practice are discussed, and three areas - examining the roles of appraisal, emotion, and culture in illness management - are identified as priority targets for further research and conceptual development.