Since its introduction in 1983, the Greek NHS is under an almost constant reform, aiming improvement on the efficiency and the quality of provided services. The national program of psychiatric reform “Psychargos” introduced new models of therapeutic approach to the care of the mentally ill, that required expansion of the existing roles and development of new roles of the healthcare staff. Consequently, the efficient management of the healthcare workforce in Greek mental facilities was identified as a primary determinant of the successful implementation of the program. Primary objective of this study was the development of a research framework for the assessment of job satisfaction in Greek Mental Health Hospitals. Among the objectives was the evaluation of the capacity of the underlying motivators and hygiene factors and the identification of potential correlations of the global job satisfaction and the motivation and retention factors with the demographic, social and occupational characteristics of the employees. A custom questionnaire was developed, based on Herzberg two-factor theory, after a systematic review of the relevant literature. The instrument was constructed by two parts and 37 items. Ten items addressed the sociodemographic characteristics of the subjects, while the remaining 27 items were distributed in 11 subscales which addressed the global satisfaction index and the “retention” and the “motivation” variables. The instrument was validated by means of the Cronbach alpha for each subscale and by confirmatory factor analysis. The study was conducted at the Public Mental Hospital of Chania (PMHC). From the 300 employees of the PMHC, 133 subjects successfully responded to the questionnaire (response rate, 44.3%). In accordance to former surveys, subjects presented average scores in the global satisfaction index (GSI). The professional category of the employee was identified as the primary determinant of the GSI. Nurses presented statistically significant lower scores in comparison to the rest of the employees. Strong Pearson correlations were detected between GSI and “working conditions”, “interpersonal relations”, “organization”, “salary” and “supervision” factors. The retention factors presented stronger impact on GSI in comparison to the motivation ones. The results of the study indicate that the proposed instrument presents satisfactory validity and reliability for the assessment of job satisfaction in Greek mental NHS hospitals.