The aim of the study was elucidation of diagnostic criteria of the nephrotic crisis in children with primary and secondary nephrosonephritis. 44 children with nephrotic crisis (59% of them had primary glomerulonephritis, 41% - secondary one) and 62 control patients with activity of nephrotic syndrome of the third degree were examined. The tested criteria were the following: the activity of the pathological process, intensity of proteinuria, level of proteinemia, albuminemia and total pool of medium mass molecules in the serum, presence of acute renal failure, diffuse cavitary edema, abdominal syndrome, migrating erycepalas-like erythemas, severe hypovolemia, thrombotic complications. The analysis of the findings show that a nephrotic crisis reflects highly active nephrosonephritis provoked by different factors including primarily hormone resistance and discontinuation of basic medication. The crisis in children is characterized by variability of the clinical picture including abdominal, hypovolemic, thrombotic, kinin and mixed variants. Early diagnostic criteria of the nephrotic crisis include the level of hypoalbuminemia, hypoproteinemia, low rate ofglomerular filtration, small volume of circulating blood and cardiac output.