With the first multicenter MCS study in Germany a research network could be established: Six environmental medicine outpatient clinics took part in the project, five of which were linked to university clinics (Aachen, Berlin, Freiburg, Giessen, Munich) and one located at a specialised hospital in Bredstedt. The department of environmental medicine at the Robert Koch-Institut (RKI) in Berlin served as the study-centre. The main focus of the study consisted of a precise description and detailed analysis of the "Multiple Chemical Sensitivity" (MCS). The causes, triggers and risk factors of MCS were to be studied. The project is based primarily on a cross-sectional design. The division of the outpatients into MCS- and non-MCS-groups also corresponds to a case-control situation with outpatient clinic based cases and controls. The specially designed documentation instruments were developed and tested in 1999.234 (80%) of the approximately 300 patients examined at the six centres in the year 2000 with completed examination instruments could be included in the study. First results will be presented. With regard to the medical assessment of MCS considerable differences between the centres were found. In the psychometric instruments self-reported MCS-patients scored predominantly in between healthy individuals and psychiatry/ psychosomatic patients.