One of the main problems in the efficiency and efficacy of an organization is its structural issue. Organizational culture is also considered as an effective factor in the performance of many organizations. The main goal of the present study was to determine the relationship of Centralization and organizational culture and performance indexes in Teaching Hospitals affiliated to Tehran University of Medical Sciences. This correlation study was performed in the year 2007. The population studied consisted of 4408 personnel from 13 hospitals among whom 441 subjects were selected and studied via a class sampling method. Data was compiled using a check list concerning the evaluation status of Centralization and another form concerning performance indexes as well as Robbin's organizational culture questionnaire. Data were obtained from the subjects by self answering and analyzed by using descriptive statistical indexes, T- test and Fisher's exact tests. Among the organizational culture indexes of the hospitals studied, control and organizational identity was better as compared to others (mean=3.32 and 3.30). Concerning the extent of Centralization in the hospitals studied, 53.85 % and 46.15 % were reported to have upper and lower organizational Centralization, respectively. Mean ratio of surgical operations to inpatients was 40%, the mean rate of admissions per active bed was 60.83, mean bed occupancy coefficient was 70.79%, average length of stay was 6.96 days, and mean net death rate was 1.41%. No significant correlation was seen between Centralization degree, organizational culture and performance indexes in teaching hospitals Tehran university of medical sciences. (with 95% confidence interval). Due to the fact that first grade Teaching hospitals use board certified members, expert personnel, and advanced equipments and because of the limitation of patients choice and, the extent of Centralization and many organizational culture components have no significant correlation with performance indexes of these hospitals. Further research regarding structure is suggested in the future.