The paper presents a study of the impact of increasing amount of distributed generation resources (DER) on control and management of transmission and distribution systems. Paper considers how DER penetration influences frequency control during normal operational conditions. Controllability of different types of DER associated with frequency control is considered. List of power system parameters influencing frequency control is presented. Case study is based on analysis of frequency control aspects for the Baltic States power system interconnection. Methodology for analysis of DER penetration aspect is based on determination of hosting capacity – maximal level of possible DER penetration that provides efficient frequency control. Numerical results of case studies are presented in paper.