Elevated levels of serum cobalamin may be a sign of a serious, even life-threatening, disease. Diseases such as chronic myeloid leukaemia, promyelocytic leukaemia, polycythaemia vera and hypereosinophilic syndrome are often accompanied by markedly elevated levels of cobalamin in the blood. A rise in the serum cobalamin concentration is one of the diagnostic criteria for polycythaemia vera and hypereosinophilic syndrome. In haematological disorders, the increase in circulating cobalamin levels is predominantly caused by enhanced production of haptocorrin. Several liver diseases such as acute hepatitis, cirrhosis of the liver, hepatocellular carcinoma and metastatic liver disease can also be accompanied by an increase in circulating cobalamin. In liver diseases, the increase in cobalamin is predominantly caused by cobalamin release during hepatic cytolysis and/or through decreased clearance of circulating cobalamin by the affected liver. Liver disorders are not an indication for determining the serum cobalamin concentration. However, a coincidentally observed elevated serum cobalamin concentration is reason for further investigation.