Comparison of utilisation of resources between hospitals is a common procedure in benchmarking. Although to be able to compare, homogeneous groups of patients should be selected. OBJECTIVES: This paper verifies the comparison of utilisation of resources for knee procedures. METHODS: A sample of 13 hospitals was selected to compare patients who were treated for knee procedures. Only patients admitted in DRG 222 were recruited for the study. Data on utilisation of resources concerning medical procedures, medical imagery, use of drugs and clinical biology was studied. RESULTS: After data validation 2.076 patients were included in the study. Between the hospitals a significant difference in the use of resources was notified. Nevertheless a general conclusion was too confounding because of the case-mix in the hospitals. Further analysis found that the main reason was the difference in operating technique. The differentiation between groups could not be made on the basis of the ICD-9 code only. Based on the national coding system of procedures additional grouping techniques were possible. Those hospitals in which the arthroscopy is a common technique, the use of resources is significant lower in all the resource domains studied. In the use of conventional radiology, the group of patients with arthroscopy had lower correlations with the volume of resources (r=.89 vs r=.95). The analysis of operating procedures showed even more differences in the correlation between the use of resources and the group of patients (with arthroscopy (r=.409) versus without arthroscopy(r=.904 )). CONCLUSION: When the use of resources is compared between patients with knee procedures it is very important to differentiate in the technique that is used. The use of DRG and ICD-9 codes is not specific enough to make the comparison possible.