The prevalence of diabetes mellitus in the family history of 371 patients with primary glaucoma--closed-angle glaucoma, ocular hypertension and open-angle glaucoma--and 85 age- and sex-matched control subjects was determined. There was a significantly-increased prevalence of familial type 2 diabetes mellitus (non-insulin dependent diabetes mellitus) in patients with closed-angle glaucoma (p = 0.004) and ocular hypertension (p = 0.02). Primary glaucoma was not associated with familial type 1 diabetes mellitus (insulin dependent diabetes mellitus). The implications are discussed.