The first clinical classification of Balkan endemic nephropathy was elaborated by A. Puhlev et al in 1960, according to which two stages could be established in the course of the disease-compensated and decompensated. Gradually, many new data accumulated as regards the various aspects of the disease, that cannot be put into the frames of the first clinical classification. On the base of the author's own long-term complex clinical-laboratory, functional, instrumental and nephrobiopsic studies, he admits the existence of four stahes in the clinical and morphological course of the Balkan endemic nephropathy. 1. Initial stage, reflecting the onset of the morbid process. The disease, at that stage, could be diagnosed via some provoking methods or renal biopsy. Morphologically, light alterations in some glomerules were established as well as more severe ones in the cells of the proximal tubules. 2. Subclinical stage - decreet and inconstant manifestations of the disease were established with completely preserved renal function. The size of the kidneys is slightly reduced - bilaterally. The morphological alterations are localized in the glomerules, proximal tubules, small vessels and interstitium. 3. Compensated stage - with manifested renal symptomatics and considerable morphological alterations in renal parenchyma, but still preserved excretory function. 4. Decompensated stage - where the known four stages of the chronic renal insufficiency are included. The classification proposed reflects the dynamics of the advancement of the morbid process. In this way, the most adequate treatment is enabled as well as the prophylaxis and assessment of working capacity and disability of the patients with Balkan endemic nephropathy.