AIM. The analysis of incidence, clinical and morphological manifestations, and the prognosis of IgA nephropathy in the Russian population.PATIENTS AND METHODS. Six hundred cases with primary IgA nephropathy (IgAN) from 1999 to 2019 were enrolled in the single-center retrospective study. Demographic and clinical parameters, morphrology data, and the treatment were analyzed. Three hundred forty seven patients were included in follow-up study. The following outcomes were evaluated: the occurrence of complete (PR) or partial remission (CR), death from all causes, the need for renal replacement therapy (RRT). The composite endpoint (RRT or eGFR decrease ≥ 50 % from the time of biopsy) was used to evaluate the risk of IgAN progression and associated factors.RESULTS. The period-average incidence of IgAN cases was 20.5 % of all indication biopsies and 31.7 % of primary immune glomerulopathies (with gradual increase to 41,5 % in last 5 years). At the time of the kidney biopsy, the proteinuria was 2.20 (1.10; 4.40) g/24h, eGFR – 69 ± 32 ml / min / 1.73 m2. Proportions of cases with arterial hypertension and with eGFR <60 ml / min / 1.73 m2 were 75 % and 36 %, respectively. The prevalence of histological changes in accordance with the MEST-C classification was as follows: M1 – 40.5 %, E1 -22.9 %, S1-70.2 %, T1-22 %, T2 – 9 %, C1-16.7 %, C2 – 4.4 %. Combined deposits of IgA and IgM (71.1 % of cases) were more frequent compared to IgA and IgG (9,6 %). In the followup period (27 (11; 61) month), 6 deaths from all causes were registered (1.7 %). The 10-year cumulative renal survival was 75 % (by dialysis) and 55 % (by composite endpoint). PR registered in 26 % of cases, CR – 24 %. PR / CR was more frequent in patients who received immunosuppression compared with patients on renin-angiotensin system blockers only (60 % vs. 40 %, p = 0.001). In multivariable Cox regression the independent factors associated with the risk of IgAN progression were: male gender, a younger age, higher blood pressure and hematuria, lower eGFR, interstitial fibrosis/ tubular atrophy (≥50 %), peritubular capillaritis and the presence of any crescents. Compared to the cohorts of other ethnic or geographical affiliation, analyzed IgAN cases were found to have more severe clinical and morphological presentations and faster progression rate.CONCLUSION. While being the most common glomerulopathy, IgAN in the Russian population has more pronounced clinical and morphological presentations and an unfavorable prognosis.