This study investigated the influence of a number of psychological factors upon the practice and outcome of diabetic self-management among young adults with insulin-dependent diabetes mellitus. Health beliefs, perception of control and knowledge were assessed by scales and questionnaires and glycosylated haemoglobin results and clinic attendance records obtained for 263 patients. The results demonstrated that the sample members perceived that they were responsible for the control of their diabetes, that the benefits of following treatment were greater than any barriers and that they were knowledgeable about their diabetes. However, these factors were not predictive of the outcome variables of metabolic control or clinic attendance according to multiple regression analysis. Implications of these results for nursing practice and for future research are discussed.