The authors investigated the relationship between serum phosphate (S-phosphate) and the metabolic syndrome in a group of middle-aged hypertensive and normotensive men during 20-year follow-up. Fifty-six men participated. Of the original 34 normotensive men, hypertension developed in 17. In the group as a whole and in those in whom hypertension developed, there was a significant negative relationship between S-phosphate at baseline and mean blood pressure (MBP) at follow-up. A significant relationship was observed between S-phosphate at baseline and components of the metabolic syndrome in the group as a whole, in individuals with hypertension, and in individuals with the lowest S-phosphate levels at follow-up. S-phosphate at baseline predicted MBP 20 years later in a group of hypertensive and normotensive men. When grouped according to the number of components of the metabolic syndrome, individuals with the lowest serum phosphate levels had the highest number of risk factors. These findings may suggest a role of low S-phosphate in the development of hypertension and the metabolic syndrome.