The aim of the study was the examination of seasonal changes of individual mean blood pressure (BP) levels and some other 24-hour BP indices of hypertensive patients in two regions of the Russian Federation (Ivanovo and Saratov). We analyzed the data of 770 patients: 499 in Ivanovo (mean age 52±10 years, 36.3% males) and 269 in Saratov (mean age 58±11 years, 56.1% males). Ambulatory BP monitoring (ABPM) was performed twice in each patient, with the interval 6 months±7 days. A marked variability of individual seasonal BP dynamics was found. For instance, in 34% of patients, the office BP levels in winter exceeded the corresponding summer levels by >10 mm Hg. A completely opposite pattern was observed in 14% of patients. The distribution of seasonal variability of 24-hour means was slightly more homogenous. The mean values of nocturnal blood pressure fall (NBPF) were higher in winter, compared to summer (p<0.001). The mean NBPF in Saratov (6.8±7.6%) was significantly lower than the standard normal value (10%). The multivariate data analysis found a significant negative association between individual NBPF and environmental temperature. In general, all 24-hour BP variability indices were higher in Saratov than in Ivanovo; the differences were highly significant. The presented issues of seasonal BP variability are of high practical importance, which warrants further investigation in prospective studies.