Objective: To describe the prevalence of diffuse idiopathic skeletal hyperostosis (DISH) in a large population-based study of elderly Icelanders, with particular reference to weight-related factors and the metabolic syndrome. Method: The study population comprised 5321 participants aged 68–96 years (2276 males, mean ± sd age 76 ± 5 , and 3045 females, age 77 ± 6) from the AGES-Reykjavik Study. DISH diagnosis was based on computed tomography (CT) scans, and interpreted strictly by the Resnick criteria and additional suggestions for CT interpretation by Oudkerk et al. Radiology readings were taken by a radiology resident and sample readings by two experienced radiologists. Results: A diagnosis of DISH was made in 13.7% of males and 2.8% of females. There was no association with age, but a strong association was seen with the metabolic syndrome [odds ratio (OR) 2.12, 95% confidence interval (CI) 1.69–2.64, p = 3.9 × 10−11]. Among the components of the metabolic syndrome, the association with DISH was significant for the insulin resistance criterion (OR 1.66, 95% CI 1.32–2.01, p < 0.001) and the body mass index (BMI) criterion (OR 2.16, 95% CI 1.70–2.74, p < 0.001). Other weight-related variables (midlife BMI, weight, and abdominal circumference) showed similar associations. Conclusions: This study, which to our knowledge is the largest published study on the prevalence of DISH, shows an association with the metabolic syndrome, particularly with the insulin resistance and BMI criteria. This is analogous with previous reports linking DISH with metabolic causes. In this age category, we did not observe any increase in prevalence with age.