The author has studied the spread of the Balkan endemic nephropathy (BEN) according to the dispensary, clinical and post mortem data in the district of Vartza and established that the disease is met in 41 settlements of the district with a total population of 47,589. The average morbidity rate in the endemic villages is 35.9% of the population. In three villages it is over 200% in five--over 100--200% and four from 50--100%, in 25--from 2--50% and only in four villages under 2%. The author has elaborated a medico-geographical map on the base of the number of the settlements where patients with BEN are to be found. As seen from the map, the disease is met in settlements situated at the foot of the Balkan and its foothills: Vratza region of the Balkan and Veslez. It is interesting to be pointed out that certain settlements free of the disease are to be found among the endemic villages. The disease affects the village population. In the towns of Vratza and Mesdra, though situated in the center of the endemic region, no BEN patients have been found among the local population.