The aim of this prospective study was to detect primary open angle glaucoma (POAG) in its early stage in patients at a higher risk of its development, and to identify the risk group with the highest prevalence of POAG. The study was conducted at Department of Ophthalmology, Osijek University Hospital Centre, and included 250 patients divided into five groups, as follows: group 1, patients with diabetes type 1 and type 2; group 2, patients with arterial hypertension (blood pressure >140/90 mm Hg); group 3, patients with positive family history of POAG; group 4, patients with myopia between -3.0 and -8.0 diopters; and group 5, control group including patients aged 40 with no risk factors for POAG development. Study results showed that distribution of glaucoma patients was not equal across the groups. The prevalence of POAG in all patients was 5.6%, whereas in patients with positive family history of POAG it was 14%, which was statistically significantly higher than in patients with diabetes and myopia (4% both), as well as in control group. The difference was greatest in comparison to control group. There was no statistically significant difference in glaucoma incidence between the group of patients with positive family history (14%) and patients with systemic hypertension (6%). The results obtained suggest that of all risk factors analyzed, positive family history of POAG is the most important risk factor for glaucoma development in all risk groups.