As part of the oncological patient care, tumor documentation has been attributed growing importance as a means of quality assurance. The extended organ specific tumor documentation can serve to answer some specific clinical questions. The rational of the so called Patient Care Evaluation Studies (PCES) carried out by the Commission on Cancer of the American College of Surgeons in the US will be shown in this article and the objectives of an initial study being carried out in the Federal Republic of Germany simultaneously with the US-study will be demonstrated. PCES are a way to compare actual patient care with idealized recommendations of Clinical Practice Guidelines. Thus, the application of Practice Guidelines in the clinical routine as one aspect of evidence based medicine can be analyzed.