The discrimination between complementary and alternative medicine / therapies (CAM) at one hand and conventional treatment at the other hand is vague and still under controversial discussion. Furthermore, most CAM lacks evidence for effectiveness, and in some cases for some CAM potential health risks or high costs are reported. The countless methods and treatments of CAM have been categorized by National Center of Complementary and Alternative Medicine into five groups: alternative medical systems, mind-body-interventions, biologically-based therapies, manipulating and body-based therapies, and energy therapies. CAM are known and used cross-cultural and are applied to a variety of different medical conditions. Patients report manifold reasons for using CAM, which will be discussed on the sample of patients with multiple sclerosis. It was shown often, that patients use CAM without informing their attending physician. Applying CAM is essentially affected by wishes of patients for active therapy attendance, dissatisfaction with conventional treatment and negative patient-physician-relation. Therefore, the attending physician should be well informed about CAM and should be open to talk about CAM to advice the patient to his best knowledge. Otherwise the patient may move synchronously or serial into two separated therapy settings without informing his attending physician, which may cause health or financial damage.