The average dietary intake of magnesium is below recommended dietary allowances in many affluent Western countries. Prolonged low magnesium intake tends to result in hypomagnesaemia which might increase the risk of chronic diseases in elderly people. A national population-based cross-sectional nutrition survey, the Elderly Nutrition and Health Survey in Taiwan (1999-2000), was used to investigate the magnesium status and association with diabetes in the Taiwanese elderly. Dietary magnesium intake was based on 24-hour dietary recalls. Blood biochemical parameters including plasma magnesium and blood glucose were also measured. Average magnesium intake was 250 mg in men and 216 mg in women, which is equivalent to 68-70% of relevant Taiwanese Dietary Reference Intakes. The mean plasma magnesium concentration was 0.903 mmol/L in men and 0.906 mmol/L in women. The prevalence of a plasma magnesium level of <0.7 mmol/L was 0.7-0.9% in the elderly, and that of <0.8 mmol/L was 8.0-9.1%. Elderly vegans had a significantly lower magnesium intake than ovo-lacto vegetarians and non-vegetarians. Diabetic men and women had significantly higher blood glucose levels than non-diabetics. The risk of diabetes was elevated 3.25 times at plasma magnesium levels<0.863 mmol/L. There was an inverse association between plasma magnesium concentration and the prevalence of diabetes. However, no association was found between diabetes and low dietary magnesium. Taiwanese elderly persons had suboptimal levels of dietary magnesium intake, which although may be sufficient to avoid overt magnesium deficiency, may not be sufficient to reduce the risk of diabetes in the elderly. Further prospective study is required to help explain the differential results between dietary and plasma magnesium levels.