BACKGROUND: Alcohol consumption is a common behavior. Little is known about the relationship between alcohol consumption and glycemic control among people with diabetes. OBJECTIVE: To evaluate the association between alcohol consumption and glycemic control. DESIGN: Survey follow-up study, 1994-1997, among Kaiser Permanente Northern California members. PATIENTS: 38,564 adult diabetes patients. MEASUREMENTS: Self-reported alcohol consumption, and hemoglobin A1C (A1C), assessed within 1 year of survey date. Linear regression of A1C by alcohol consumption was performed, adjusted for sociodemographic variables, clinical variables, and diabetes disease severity. Least squares means estimates were derived. RESULTS: In multivariate-adjusted models, A1C values were 8.88 (lifetime abstainers), 8.79 (former drinkers), 8.90 (<0.1 drink/day), 8.71 (0.1-0.9 drink/day), 8.51 (1-1.9 drinks/day), 8.39 (2-2.9 drinks/day), and 8.47 (>/=3 drinks/day). Alcohol consumption was linearly (p < 0.001) and inversely (p = 0.001) associated with A1C among diabetes patients. CONCLUSIONS: Alcohol consumption is inversely associated with glycemic control among diabetes patients. This supports current clinical guidelines for moderate levels of alcohol consumption among diabetes patients. As glycemic control affects incidence of complications of diabetes, the lower A1C levels associated with moderate alcohol consumption may translate into lower risk for complications.