BACKGROUND: There have been few prospective studies on diet and glucose abnormalities as determined by oral glucose tolerance test. METHODS: To investigate the impact of dietary factors on the development of glucose intolerance including diabetes and impaired glucose tolerance, we performed a follow-up survey of 1, 075 subjects aged 40-74 years of normal glucose tolerance from 1988 through 1993/1994 by repeated 75 g oral glucose tolerance test and dietary survey. Information on habitual food consumption was obtained using a semiquantitative food frequency method. RESULTS: Of the total subjects studied, 119 (11.1 %) developed impaired glucose tolerance and 24 (2.2 %) developed diabetes during the follow-up. At baseline, the age-adjusted amount of alcohol intake was significantly higher in males who developed glucose intolerance than in those who did not (26.7 g vs. 15.7 g, p<0.05), while the polyunsaturated/saturated fatty acids (P/S) ratio was significantly higher in females with future glucose intolerance (1.42 vs. 1.31, p<0.05). Among the female subjects who developed glucose intolerance, the intake of animal fat less decreased during the follow-up period compared with normal subjects, resulting in a significant decrease in the P/S ratio (-0.09 vs. 0.05, p<0.05). In a multiple logistic regression analysis, alcohol intake at baseline for males and decreased P/S ratio during the follow-up for females remained a significant risk factor for glucose intolerance inde- pendent of other dietary and non-dietary factors as well. CONCLUSIONS: These results suggest that a high intake of alcohol and a decreased P/S ratio contribute to the risk of glucose intolerance in contemporary Japanese. J Epidemiol 2003;13:251-258.