['Whether health literacy is independently associated with processes or outcomes of diabetes-related care is controversial. We tried to demonstrate the interaction of health literacy and understanding of health education and instructions in achieving glycemic control.', "Five hundred and one consecutive patients with type 2 diabetes mellitus (DM) in the outpatient clinic of the metabolism department were recruited into this pilot study. The demographic data were collected from patients' self-reports. The clinical background information was collected through electronic medical records. A questionnaire derived from part of the Mandarin Health Literacy Scale was used to measure numeracy and functional health literacy of people with diabetes. Health literacy levels were categorized into inadequate, marginal and adequate. Patient self-ratings of their perceived understanding of the health education information and instructions provided by their case manager in the past were categorized into two subgroups: better and poor. Patients with an HbA1c level equal to or below 7% were considered to have good glycemic control. Multivariate logistic regression was used to find associated factors of health literacy and understanding of health education and instructions. GENMOD procedures were used to analyze repeated outcome measurements of glycemic control.", 'Higher educational attainment and higher household income (odds ratios were 2.23 and 2.22, respectively) were significantly associated with patients who had adequate health literacy. Higher educational attainment and patients with a family history of DM (odds ratios were 4.99 and 1.85, respectively) were significantly associated with better understanding of health education and instructions. Adequate health literacy is not the only factor associated with good glycemic control. The effect of adequate health literacy in achieving good glycemic control might be masked by patients with better understanding of health education and instructions.'] Does patient perception of understanding health education and instructions have moderating effect on glycemic control?