Immediate type allergic reactions to vitamin B12 is a rarely encountered condition. Commercial preparations of vitamin B12 (cyanocobalamin and hydroxycobalamin) can lead to Type 1 hypersensitivity reactions. Allergic reactions to vitamin B12 may consist of urticaria, angioedema and anaphylaxis. Some patients develop an allergic reaction to a derivative of vitamin B12 and can tolerate the other commercial form. Allergic reactions may sometimes occur against both compounds of vitamin B12.

We presented a case of cyanocobalamin allergy who could tolerate hydroxycobalamin. Cyanocobalamin allergy and hydroxycobalamin tolerance was demonstrated by provocation tests. In this case report, it is emphasized that an allergic evaluation including provocation tests should also be done in patients with suspected allergy to vitamin B12 in addition to skin prick tests and intradermal (ID) tests.