Renal damage in patients with rheumatoid arthritis (RA) is the most frequent and serious among other systemic manifestations and holds a special place in connection with a significant impact on prognosis and approaches to therapy. Today we know that one of the main possible factors of occurrence and development of RA are external trigger factors, among which the most important factor are infectious, and its pathogenic effect on the body can be done in different ways. Based on the latest scientific evidence on the importance of infectious trigger factors in the manifestation of RA, chronic pyelonephritis among these triggers is one of the leaders. Great interest is also the probability of pyelonephritis manifestation while presence of RA. The aim: to identify predictors ofpyelonephritis manifestation in patients with rheumatoid arthritis. Materials and methods. The authors examined 31 patients with RA with presence of chronic pyelonephritis (CP), 31 patients with RA without presence of CP and 20 healthy individuals. Was used clustering and classification methods of Data Mining on indicators of lipid peroxidation of blood and urine, р2–microglobulin blood and urine, immune factors, that defined progressive CKD on the results of our previous studies (IL–1p,IL–10, TGF–р). Results. Found that patients with diagnosed RA only, mainly are included in the cluster «1» (18patients). Some of them (3 persons) classified as belonging to the cluster «2». Thus, these individuals should have two signs of disease, RA and CP, despite the fact that they have only diagnosed RA. It means that these patients are at risk of developing CP. This analysis gives grounds to consider that RA may be signs of a factor that causes manifestation of CP. It is proved that the main factor that characterizes the individuals belonging to the cluster of healthy is 2– microglobulin in the urine with the same threshold value, but factor in determining membership of a type of disease is a factor MDA of urine. Conclusion. The main predictors of pyelonephritis manifestation in patients with rheumatoid arthritis were 2– microglobulin and MDA in urine and TGF– 1 in blood. A new method of diagnosing ofprognostic factors of CP manifestation in patients with RA which is based on cluster and classification analysis makes it possible to establish the interrelation between a diagnosis of RA and caused by it manifestation of CP.