OBJECTIVE: To assess the association of 1,5-anhydroglucitol (1,5-AG) with 2-h postprandial glucose values in type 2 diabetic patients followed over 12 months in an outpatient setting. RESEARCH DESIGN AND METHODS: In 55 patients, we examined self-measured postprandial blood glucose values for correlations with 1,5-AG values over prespecified preceding time periods (3 days, 1 week, and weekly up to 12 weeks). RESULTS: The correlation coefficients for postprandial glucose values were -0.34 (P < 0.05) for 3 days, -0.38 (P < 0.001) for 1 week, and -0.40 (P < 0.001) for 2 weeks preceding the measurement of 1,5-AG. Correlations declined for time periods >2 weeks before measurement of 1,5-AG. The correlation was lower with fasting/preprandial plasma glucose levels. There was no time dependency for the correlation between A1C and fasting or postprandial glucose. CONCLUSIONS: 1,5-AG best reflected the 2-h postprandial glucose values of the 2 previous weeks.