In the present paper the interrelation between the potato crop yields and the excessive and insufficient soil water status in the years 1972-1995, both in the whole country and in the provinces, is determined. There was also an attempt to determine the decrease in the potato crop yields caused by the extreme soil water status expressed by means of the Wug index according to Koźmiński, throughout Poland. This relationship was described by means of single regression analysis, using the STATISTICA 5 program. The decrease in the national potato crop yields to soil water status value lower than the multi-year average, resulting from the extreme moistening of soil in the period from 21st June to 20th August expressed by means of the soil moistening index occurred at Wugn index > 2.8 for insufficient moistening of soil and at Wugm index > 0.6 for excessive soil moistening. The risk to potato crops in Poland caused by excessive moistening of soil during the period from 21st June to 20th August was, on average, 3% lower than that resulting from insufficient soil moistening. The latter may be the cause of a decrease in the yields to a value 10% lower than the multi-year average. The spatial distribution of the potential lowering of potato crops due to insufficient soil moistening showed that the largest risk was in the central part of the country, whereas the greatest danger due to excessive moistening of soil was in the south eastern fringes of the country and in the hills of Pojezierze Pomorskie (Pomeranian Lake Region).