Most MS patients use unconventional therapies, usually as complementary measures in addition to the conventional treatment. Only a few adequate clinical trials exist in this field. By definition, the efficacy of these therapies is unproven. Moreover, the possible risks are also largely unknown. Some therapies rely on rational pathophysiological considerations, other must be regarded as potentially harmful. The influence of diet on MS is unproven. Possibly, unsaturated fatty acids are beneficial. However, a few randomized trials yielded inconclusive results. Long-term supplementation of Vitamin D is associated with a decreased MS incidence. There is, however, insufficient evidence for an influence of Vitamin D on the course of the disease. Because of the high prevalence of osteoporosis in MS patients, prophylaxis with Vitamin D and Calcium is widely accepted. The effects of various minerals, selenium, antioxidant compounds, fish oil or vitamins remain speculative.