A series of scales was designed to measure perceived control of diabetes and diabetes-related health beliefs with a view to predicting treatment preferences and individual differences in response to the treatments. Scale development is described and the psychometric properties examined with responses from 286 insulin requiring adult diabetic patients. Patients were significantly more likely (p less than 0.001) to attribute responsibility for their diabetes control to themselves rather than to their medical advisors or to other factors. For most of the patients the benefits of treatment were perceived substantially to outweight any barriers (p less than 0.001). Compared with their perceptions of vulnerability to disorders unrelated to diabetes, patients thought that they were more vulnerable to such diabetes related complications as eye, kidney and foot problems (p less than 0.001) but not to heart disease.