Purpose: The paper aims to investigate the degree of employee satisfaction from the use of the information systems taking as an example the employees from the Electronic National Social Security Fund in the Prefecture of Attica, Greece. Design/Methodology/Approach: At a theoretical level, a new model was formed based on the synthesis of two others from the literature, forming in this way an innovative research approach. To conduct empirical research, the quantitative method was chosen through the use of a structured questionnaire. For the analysis of the results, methods and techniques of both descriptive and inductive statistics were used. Findings: The results show that the overall degree of users’ satisfaction with the existing information systems directly depends on the degree of satisfaction that users receive from the individual independent variables of the proposed combined evaluation model (system quality, information quality, service quality, perceived ease of use and perceived usefulness). Practical Implications: The results of this research can be used by organizations in the public administration sector to redesign the existing information systems aiming to increase the organization’s efficiency and effectiveness through increased employee satisfaction. Originality/Value: In the existing literature, studies in which an information system is evaluated by employees as users of these systems are limited. This study searches to fill the gap that exists in the bibliography.