OBJECTIVE: We prospectively assessed whether the combined measurements of fasting plasma glucose (FPG) and A1C were effective for predicting type 2 diabetes. RESEARCH DESIGN AND METHODS: Study participants included 6,736 nondiabetic Japanese men aged 40-55 years. Type 2 diabetes was diagnosed in those who had an FPG >or=126 mg/dl or who were being treated with an oral antidiabetic agent or insulin. The models including FPG, A1C, and both were compared using the area under the receiver operating characteristic (AUROC) curves. RESULTS: During the 4-year follow-up period, we confirmed 659 diabetes cases. In multivariate analysis, both FPG and A1C were independently associated with the risk of type 2 diabetes. The model including both FPG and A1C had a greater AUROC curve than that including FPG alone (0.853 vs. 0.818; P < 0.001) or A1C alone (0.853 vs. 0.771; P < 0.001). CONCLUSIONS: The combined measurement of FPG and A1C was effective for predicting type 2 diabetes.