Aim — to study the reasons of intraocular pressure (IOP) resistance to therapy in patients with glaucoma. Material and methods. During the period 2011—2013 we examined 72 primary glaucoma patients (stage I—III), 44 women and 28 men, aged 49—87 years (65.2±2.5 years on average) referred by local ophthalmologists due to poor response to hypotensive therapy. Results. We suggest that glaucoma should be regarded as resistant if, despite combination therapy with three antihypertensive drugs at optimal doses, IOP stays above the target. In the present study, the treatment was found suboptimal in 19.4% of cases. About 45% of all patients (33 patients) demonstrated poor compliance to the prescribed treatment. Resistant glaucoma, as we have defined it, was diagnosed in 33% of cases (pigmentary glaucoma, pseudoexfoliation glaucoma, secondary unrecognized glaucoma, etc.). This group also included patients, in whom b-blockers were initially effective, but then seemed to lose their power. Conclusions. 1. The reasons for intraocular pressure to resist hypotensive therapy are often associated with medical inertia (inaccurate diagnosis, inadequate treatment, etc.) and lack of patient compliance. 2. Resistant glaucoma in its true sense accounts for about 35% of cases of IOP being above the target despite conservative treatment. 3. It is advisable that at the time of first presentation, any patient who fails to reach the target IOP is treated as an «uncontrolled glaucoma» case, until the reasons for his/her resistance are clear.