Background and Aim: Organizational centralization, an important concept/system in management, relates to hierarchy of authority and degree of participation in decision-making. In this study we aimed to determine the extent of organizational centralization in hospitals affiliated with Tehran University of Medical Sciences (TUMS), Tehran, Iran and identify factors affecting the organizational centralization at the level of executive managers.Methods and Materials: All the managers and head nurses of 13 TUMS hospitals (26 subjects) were included in this cross-sectional study in 2005. Data, collected using questionnaires, were analyzed using the following tests: t-test, ANOVA, Pearson and Spearman, the software being the SPSS. The extent of organizational centralization was categorized into centralized, semi-centralized, and uncentralized.Results: Five of the 5 variables studied were statistically significantly associated with organizational centralization. They were gender (p=0.001), organizational position (p=0.005), attending management courses (p=0.001), and financial burden of decisions (p=0/03) in the hospital managers group, and possibility of controlling the decision (p=0.014) in the head-nurses group. Conclusion: The average organizational centralization in the hospitals was 75.38%; it was 76.3% and 73.38% for hospital managers and head-nurses, respectively. On the whole, the management system of TUMS hospitals is a semi-centralized system.