The paper determines genetic factors of earth hummocks that are found below the lower limit of the periglacial processes. This issue was analyzed in the area of Vlasina and Krajište, where seven localities with earth hummocks and one locality with palsa mounds. Genetic factors have been classified into two groups: inherited factors (geological composition, temperature fluctuations, vegetation, hydrogeological regime) and additional factors, such as human activities which led to changes of ecological balance and microclimatic characteristics.