Based on a Med-line search, the clinical, scientific, historical and philosophical aspects of the Chronic Fatigue Syndrome are reviewed. The review shows that scientific research into CMS lacks coherence. Parallels and relations with depression are analyzed. Finally, different levels of meaning are differentiated and the legitimizing character of clinical-diagnostical statements is analyzed. The current confusion surrounding CFS is related to implicit differences in views concerning medicine's task. As a new diagnostic category CFS offers insight into the status and relation of clinical practice and scientific research.