This article examines the relationships among hospital structural characteristics, individual physician characteristics, medical staff organization characteristics and quality of care for two conditions: acute myocardial infarction and appendicitis. Using data obtained from the Commission on Professional and Hospital Activities (CPHA), approximately 50,000 acute myocardial infarction cases and 8,183 appendectomy cases collected from 96 hospitals in the East North Central Region of the country (Illinois, Indiana, Michigan, Ohio and Wisconsin) were examined. These data were merged with medical staff organization and related data on hospital characteristics obtained from the American Hospital Association. The results indicate that such medical staff organization factors as involvement of the medical staff president with the hospital governing board, overall physician participation in hospital decision making, frequency of medical staff committee meetings and percentage of active staff physicians on contract are positively associated with higher quality-of-care outcomes, independent of the effects of hospital and physician characteristics. Further, the medical staff organization factors appear to be somewhat more strongly associated with higher quality-of-care outcomes than the hospital and physician characteristics. For acute myocardial infarction, higher volume of patients treated per family practitioner and internist and presence of a coronary care unit were also associated with better outcomes. Given the restricted number of conditions studied, the geographically limited sample and the fact that specific variables were not consistently related to quality of care for both conditions, the results area viewed as preliminary. However, they are consistent with and extend other developing findings in this area. They also suggest that more attention needs to be given to the organization of the hospital medical staff and its articulation with the overall hospital decision-making structure and process in attempts to improve outcomes of hospitalization.