Investigating the existence of volume-outcome relationships for specific disease groups relates directly to the policy issue of whether, and how, specific inpatient services should be regionalized. This study examined whether medical costs and lengths of stay as outcomes were affected by changes in volume within hospitals. Based on the claims data obtained from National Federation of Medical Associations, each six disease categories from medical and surgical conditions were selected and 29,720 cases from 1,266 hospitals were analyzed. Main findings of the research can be summarized as follows: 1. Analyzing volume and cost per case relationship, tonsillectomy class 1, hernia procedure class 0, appendectomy and cesarean section class 0,1 in surgical conditions showed negative relationship significantly. In cases of medical conditions, costs per case in respiratory neoplasm class 2, COPD class 1, 2, digestive malignancy were also related to volume negtively. 2. Comparing volume with length of stay per case, lens procedure class 0, hernia procedure class 0, appendectomy class 0,1, cesarean section class 1 in surgical conditions showed negative relationships significantly. In medical conditions, volume of respiratory neoplasm class 2, COPD class 1,2, digestive malignancy class 0 were associated with negatively. 3. Within same disease categories, changes in cost and length of stay per case to volume were more remarkable in severe cases. These results suggested a significant inverse relationship between disease cases and cost, length of stay per case as outcome variables.