Procedure volume has been used as a proxy for quality and recommended as a basis for hospital referrals. We studied the volume, mortality, and associated hospital and staffing characteristics of ten complex procedures in U.S. hospitals using the 2000 HCUP Nationwide Inpatient Sample. Although the majority of patients had their procedures performed in high-volume hospitals, for seven procedures, more than three-fourths of hospitals would be considered low-volume. Unadjusted mortality rates were significantly higher at low-volume hospitals for five procedures. Low-volume hospitals also tended to have lower mean numbers of residents and RNs. However, for two procedures, low-volume hospitals had RN and resident staffing equal to or higher than those of high-volume hospitals, and the unadjusted mortality rates were no different.