Vitamin B deficiency causes many diseases, which may be improved by vitamin B supplementation. Homocysteine, a sulphur amino acid, is frequently increased in patients with vitamin B deficiency, chronic renal failure and metabolism disorders. Bone and cardiovascular disease is often detected in patients with renal disease or homocystinuria. This review shows the most important discoveries, including recent patents, about vitamin B therapy not only in hyperhomocysteinemic patients but also in the general population. Vitamin B supplementation may be useful to reduce bone and cardiovascular events, but until now prospective intervention studies have given uncertain results. We need well-done randomized controlled trials to verify the effects of vitamin B treatment on these hard end-points.