BACKGROUND: Little is known about the aetiology of glioma. Research is often hampered by the low incidence and high mortality of the disease. Concomitant diseases in glioma patients may indicate possible aetiological pathways. We therefore studied comorbidity in glioma patients. PATIENTS AND METHODS: We performed a case-control study using population-based data from the Eindhoven Cancer Registry. We compared prevalences of concomitant diseases in 510 glioma patients with two reference cancer populations from the same registry. RESULTS: Compared with all other cancer patients, a significantly higher prevalence of hypertension was found in glioma patients for age categories 60-74 years [odds ratio (OR) 1.37; 95% confidence interval (CI) 1.02-1.84] and 75+ years (OR 2.37; 95% CI 1.34-4.21). The association was most pronounced in elderly men and in astrocytic glioma, with a maximum in age category 75+ years (OR 5.86; 95% CI 2.20-15.7). The prevalence of cerebrovascular disease was higher in glioma patients >45 years old (OR 1.67; 95% CI 1.12-2.47), whereas the prevalence of other cancers was lower (OR 0.64; 95% CI 0.48-0.87). No consistent associations were detected for several other concomitant diseases. CONCLUSIONS: Our data suggest an association between hypertension and glioma, although questions remain about causality and the possible mechanisms. We hypothesise that this association is mediated through potentially neurocarcino