Obesity is a frequent co-morbid condition associated with diffuse idiopathic skeletal hyperostosis (DISH). Serum growth hormone (GH), insulin-like growth factor (IGF-1) and insulin are significantly elevated in patients with DISH. In this study, we examined the relationship between body mass index (BMI) and basal serum GH, IGF-1, and insulin concentration in a group of 36 DISH patients. Basal serum insulin levels were significantly elevated (P<0.001) in DISH patients with a BMI>28 kg m(-2), classified as obese, compared with DISH patients with BMI ranging from 23 to 28 kg m(-2). In addition, BMI strongly positively correlated with serum insulin concentration in DISH patients (adjusted r2 = 0.348, P<0.001). However, BMI did not correlate with either basal serum GH (adjusted r2 = -0.013) or IGF-1 levels (adjusted r2 = -0.010) in DISH. We conclude that BMI does not seem to contribute to elevated serum GH and IGF-1 levels in symptomatic DISH.