A powerful hospital information system (HIS) contains information about diagnostic and disease data of all patients in a hospital. In the university hospital in Frankfurt / Main Germany more than 80% of all wards are completely "paperless". But the identification of patients for clinical trials is very difficult. We developed a special query and reporting tool in the HIS to recognize patients with a specific disease and with basic inclusion and exclusion criteria for a specific clinical trial. With the help of this query tool it is possible to increase significantly the patient numbers for clinical trials in a short period.