The insulin response after a glucose challenge was studied in 11 male patients with diffuse idiopathic skeletal hyperostosis (DISH) and in 8 age, sex and weight matched controls. There was significant hyperinsulinemia in the DISH group, most marked at 2 h after the glucose challenge. Growth hormone levels were found to be normal in each group. The marked hyperinsulinemia in patients with DISH may play a role in the pathogenesis of this condition.