Although adherence to treatment regimes is clinically important in diabetes mellitus, the best way to improve it is unclear. As a precursor to evaluating the place of a brief intervention (motivational interviewing) in the treatment of diabetes, this study investigated the relation between motivation and glycemic control in 361 diabetic out-patients. Outcome measures were the Stages of Change Readiness and Treatment Eagerness Scale (SOCRATES) and HbA1C level--a measure of glycemic control. The majority of patients (86.7%) could be allocated to a single motivational stage, indicating that this concept is applicable in the study of diabetes. There were significant associations between HbA1C level and motivational stage, but not in the direction predicted. That is, patients at an earlier motivational stage had lower HbA1C levels than those at later stages. The results suggest that feedback of HbA1C level may partly determine the patient's motivation to control their diabetes, although the effect is quite weak.