Glaucoma is the second leading cause of blindness in the world after cataract, affecting approximately 70 million people. Glaucoma affects people of all ages including children, but mostly older people. The purpose of this study was to determine what patients with glaucoma know about glaucoma and whether the knowledge about glaucoma is related to age, gender, education and family history. The study included 170 glaucoma patients recruited from the Cabinet for Glaucoma, Department of Ophthalmology, University Hospital Sestre milosrdnice in Zagreb. The data were collected by means of a questionnaire consisting of 39 items about glaucoma-course of the disease, its symptoms, therapy, side effects and 9 items about sociodemographic data including family history, cause of hospitalization and type of glaucoma. The data were quantitatively analyzed using appropriate statistical methods. According to the results, there are no statistically significant correlations between knowledge and age, age of onset, gender, education nor family history. However the answers to questionnaire items showed that glaucoma patients are well informed about main glaucoma facts (for example, 92% of patients said that the chance of getting glaucoma was higher if intraocular pressure is increased) while the most common answer to questions related to treatment and type of glaucoma was “I don’t know” (for example, to the statement that some eye drops should not be used by cardiac or asthma patients 52.9% patients responded with “I don’t know”; and to the statement that the most common type of glaucoma is open-angle glaucoma, 58.8% patients also responded that they didn’t know). It is interesting that 50% glaucoma patients consider that eye drops can repair the damage caused by glaucoma. Also, only 18.2% patients were familiar with glaucoma before they were diagnosed.