In the study data from nine meteorological stations from the region of Central and Eastern of Poland (1971-2005) were used. They were monthly sums of precipitation and average monthly air temperatures during the growing season of late potato (V-VIII). Optimum rainfall for late potato acc. to the Klatt index (after Grabarczyk 1983) was calculated for the medium concise soil and light soil in the subsequent months of the growing season. From the differences between the values ​​of monthly sums of precipitation occurring in the research years and the values recognised as optimal the rainfall deficit and excess were determined. It was found that during the growing season of late potato the deficits were twice more frequent than the excess of rainfall. The average long-term sum of precipitation deficiency during May-August on light soil was more than 140 mm, and on the medium concise soil more than 100 mm. The values ​​of excess rainfall during this period on both soil types were at a similar level and amounted to more than 100 mm. The greatest deficiency of rainfall was recorded in July and August. Extreme rainfall deficits (higher than the average multi-annual) occurred with the greatest frequency on light soil.