The case loads of 11 teaching and 20 nonteaching hospitals are compared, using the original 383 diagnosis-related groups (DRGs) to analyze the extent to which case-mix differences contribute to differences in average cost per case. Case-mix differences are concentrated in a small proportion of DRGs. Teaching hospitals have relatively more surgery cases and neoplasms, and nonteaching hospitals have more cases with heart conditions and infectious diseases. Most nonteaching hospitals have a similar case mix, but among the teaching hospitals, there are two distinct case-mix types, one with which only teaching hospitals are correlated, one that correlates with both teaching and nonteaching hospitals. The average cost per case is more than 60% more expensive in teaching hospitals. Only approximately one quarter of this higher cost is accounted for by case-mix differences. The rest results from the fact that patients in the same DRGs cost more, on average, in teaching than in nonteaching hospitals.