OBJECTIVES: Variations in disease treatment and costs for US Colorectal Cancer (CRC) patients may be explained by factors beyond characteristics of disease and treatment. Patient characteristics may impact CRC treatment and costs. The aim of the study is to investigate whether patient characteristics such as payor, gender, and age impact inpatient health care resource use and costs for US CRC patients. METHODS: Primary study endpoints - hospital length of stay (LOS) and average daily charges (ADC) among CRC patients were examined using data from Health Care Utilization Project (HCUP) Nationwide Inpatient Sample. Hospital discharges from 1993-1999 with principal discharge diagnosis of CRC were included. All charges were expressed in 2000 US dollars. Ordinary least square (OLS) models with log transformation of LOS and ADC were developed. Covariates were: gender, primary payor, age, year, and teaching hospital. Disease-specific risk factors were also included as potential confounders. RESULTS: We identified 213,875 CRC discharges. The mean LOS and ADC for the reference groups were: 9.9 days and $2878 for male; 8.5 days and $2944 for HMO; 9.9 days and $2875 for patients aged £ 54 years; 9.9 days and $2775 for non-teaching hospital; and 11.5 days and $2589 for the year 1993. Semi-log OLS models, after controlling for other covariates, indicated that female, Medicare, Medicaid, self-pay, older people, and teaching hospital were associated with longer LOS (P<0.0001); female, Medicaid, Medicare, self-pay were associated with lower ADC, while teaching hospital was associated with higher ADC (P<0.0001). Adjusted LOS declined at an annual rate of 3.7%, while ADC grew annually at 2.5%. CONCLUSIONS: Patient characteristics contributed to the variation of inpatient resource use for CRC patients. This association provides health care policy decision-makers information regarding treatment practices. Further research should examine whether the association is observed for other tumors and disease areas.