Twenty-five Type 1 diabetic patients and their spouses attending a diabetes clinic completed the recently developed CCQ-1 questionnaire, which assesses knowledge about the disease. Questionnaires were completed in the presence of a clinical psychologist. Glycosylated haemoglobin concentration was inversely correlated with patient scores for general management (r = -0.69, p less than 0.001), insulin (r = -0.66, p less than 0.001), home monitoring (r = -0.53, p less than 0.01), and overall knowledge (r = -0.55, p less than 0.01), but not for diet and footcare. No association was found between patients' metabolic control and scores among spouses, who knew significantly less about the disease than the patients themselves. The strength of the associations found supports the use of well-designed psychological instruments in diabetes research.