Objective: To determine the role of regulatory cells in patients with vulgar psoriasis (VP) and to provide evidence of its possible use for diagnosis, treatment, and measurement of therapeutic effectiveness. Materials and methods: We studied 60 patients (35 women and 25 men) with VP (28 patients suffering from an advanced phase of vulgar psoriasis, 19 with remedial, and 8 with retrogressive disease phase). 42 patients suffered from VP for less than 20 years and 28 participants for 20 years and longer. Patients were also divided into three groups: with mild (10 patients), moderate (22 patients), and severe (28 patients) VP. The amount of Tregs was also examined prior to and after the narrow-band UVB phototherapy in 12 patients’ vulgar psoriasis advanced phase. The group of healthy donors (HD) consisted of 22 persons. Participants' age ranged from 18 to 55 years. Results: We have shown the reduced number of CD4+CD25+Foxр3+CD127LOW Tregs in peripheral blood of patients with VP (2,84±1,00% for patients with VP and 4,02±0,73% for HD), and an increase in their number over the phase transition (2,59±0,68% for advanced phase, 2,82±1,55% for remedial and 3,68±1,62% for retrogressive phase). The inverse correlation was found not only between the number of Tregs and the VP severity level (r=-0,39) but with the disease duration as well (r=-0,46). We also showed that NB-UVB phototherapy promotes the increase of Treg cells amount.