Chronic renal insufficiency (CRI) is an irreversible lesion of the renal function with advancing of renal rickets, dyselectrolythemia, azotemic osteodystrophia in the bones. On the background of all those severe changes in organism, low indices of dental caries epidemicty are cited in literature. A total of 30 children with CRI were examined: Group 1--21 children with disease onset immediately after birth and duration from 5 to 15 years and group 2--9 children with disease onset after the age of 7 and duration from 2 to 5 years. The intensity of caries and epidemicty were compared according to milk and permanent teeth with a group of healthy children (900). A four-time higher urea level was established in group 1, reduced calcium and increased phosphorus. The children with CRI were less affected by dental caries as compared with the healthy ones, being better manifested in case of an earlier onset and longer duration of the disease. The problem of the future is the explanation of the phenomenon observed and the results--used in prophylasxis.