Fatigue is an enigma: Everyone seems to know what it is, but a detailed definition is hard to provide. Like water, it slips away and cannot be grasped. There are no laboratory tests, no magnetic resonance image can quantify it objectively, and no specific treatment is available. Fatigue is a common and often severe complaint. In the adult US population, 9.4% have fatigue during at least one month1, and as many as 22% of working adults were fatigued in The Netherlands2, as summarized in the article by Bergman, et al in this issue of The Journal 3. When a patient with rheumatoid arthritis (RA) starts talking about fatigue, the doctor will look for anemia, hypothyroidism, and other treatable explanations first. But when fatigue persists, the doctor does not know what to say: as a patient with RA recently told me, “Doctors do not seem able to understand or to handle fatigue, so despite the fact it is one of my main problems, I stopped talking about it in the clinic.” This fits in with the findings of a postal questionnaire among Dutch rheumatologists4, and with in-depth studies in UK patients, most of whom did not discuss fatigue with their clinicians, but when they did they felt it was dismissed5. Fatigue is a significant problem for people with rheumatic diseases as it contributes to many aspects of life. Studies have found the prevalence of fatigue in RA patients to be 88%—98%6. Patients with osteoarthritis (OA) experience notable amounts of fatigue and indicate it has substantial impact on their lives7. Fatigue can be both physical and cognitive, manifesting as inability to think clearly, concentrate, or be motivated to do anything5. Patients perceive their fatigue as unmanageable and … Address reprint requests to Prof. Rasker. E-mail: J.J.Rasker{at}utwente.nl