The work is based on data on monthly air temperatures, monthly sums of atmospheric precipitation and early potato yields in 2000–2013 obtained from seven COBORU (Research Centre for Cultivar Testing) stations situated in east-central Poland. Hydrothermal conditions during the growing season (April–July) of early potato were described by means of the Sielianinow’s coefficient. The relationships between potato yields and the Sielianinow’s hydrothermal coefficient of the growing season were examined using multiple regression equations generated by means of the step-wise regression procedure followed by polynomial regression procedure. The average Sielianinow’s coefficient values ranged from 1.43 in April to 1.66 in May during the early potato growing season in east-central Poland. The applied statistical methods revealed that the hydrothermal factors impacted on early potato yields, particularly in the second stage of potato growth and development.