Purpose: to establish risk factors of masked uncontrolled hypertension (MUCH) and clarify how fixed combinations can affect blood pressure (BP) control. Methods: We examined 70 patients with hypertension. The initial assessment of the effectiveness of antihypertensive therapy was carried out 3 months after its appointment. Of the 70 patients, 63 were able to reach essential office BP reduction point (these patients were additionally scheduled for ABPM). Results: Among 63 patients in whom hypertension was controlled according to office BP data, 58.7% had insufficient BP control according to ABPM data. Among patients with insufficient control of out-of-office BP, there were significantly more patients with circadian rhythm disorders (p=0.000). An assessment of possible factors for the development of MUCH showed that elderly age occurred in 78.4%, male sex - in 59.5%, smoking - in 70.3%, stress - in 78.4%, various sleep disorders - in 45.9%, diabetes mellitus (DM) - in 56.8%, obesity - in 67.6%, insulin resistance (IR) - in 73%, chronic kidney disease (CKD) - in 35.1% patients with MUCH. Analysis of patient therapy showed that out of 37 patients with MUCH, 7 patients received monotherapy, 9 patients - free dual combinations, and 21 patients - fixed dual combinations. For patients with MUCH, antihypertensive therapy was strengthened: patients who had previously received monotherapy or free combinations were transferred to double fixed combinations (both drugs acted for 24 hours), and those patients who received double fixed combinations were transferred to triple fixed combinations. Evaluation of therapy after 3 months showed that of 37 patients with initially established MUCH, complete BP control was achieved in 86.5% (in the remaining 13.5%, despite sufficient office BP control, MUCH was maintained according to ABPM data). Conclusions: In inadequate control of out-of-office BP, disturbances of the circadian rhythm are more common than with complete BP control. MUCH is associated with such risk factors as elderly age, male gender, smoking, stress, sleep disturbances, DM, obesity, IR, and CKD. Strengthening antihypertensive therapy contributed to the achievement of both office and out-of-office BP in 86.5% of patients with previously established MUCH.