The purpose of this study was to characterize the barriers to tight control of diabetes mellitus. The study collected data from multiple sources at a primary health care clinic in an academic teaching hospital serving an urban population, including patients' charts, structured interviews with patients, a survey of physicians' general perspectives and beliefs concerning diabetes mellitus, and a physician's structured review of barriers to tight control for individual patients. One hundred thirty-five patients with scheduled appointments were eligible for the study, of whom 94% had had a recent hemoglobin A1C (HbA1C). Seventy-seven of 88 patients (88%) who presented for their appointments consented to the interview, 48 of 50 providers (96%) returned useable surveys, and providers completed individual assessments for 96 patients (71%). Patients had a mean age of 61 years, an average of 7.60 diagnoses, and an average of 8.96 prescriptions. Their diabetes control was less than ideal, with less than 15% having normal or near normal control and almost a quarter having poor control. Correlations of HbA1C with age and show rate were seen. Physicians' assessments showed that motivation and understanding of diabetes and compliance with diet and medications correlated with diabetes control. Neither patient knowledge nor physician knowledge appeared to be a problem, nor did either correlate with diabetes control. The number of barriers to control were many, with over half of the patients having five or more barriers. Tight control of blood glucose is felt to be an important aspect of quality care for diabetic patients. In this study, a representative sample of diabetic patients had less than ideal diabetes control. This population was receiving their care in an urban setting and had many comorbid illnesses and many barriers to control. Age, motivation, understanding of the disease, show rate, and compliance with diet and medications had statistical correlations with diabetes control. In order to improve the quality of care for diabetic patients, barriers to care must be addressed.