Folic acid and cobalamin are B-group vitamins that play an essential role in many cellular processes. Deficiency in one or both of these vitamins causes megaloblastic anaemia, a disease characterized by the presence of megaloblasts. Megaloblasts occur when inhibition of DNA synthesis causes asynchronous maturation between the nucleus and the cytoplasm. Clinical manifestations are similar to those of other types of anaemia, with the exception of cobalamin deficiency megaloblastic anaemia, which presents distinctive neurological symptoms. An understanding of the metabolism of these vitamins will enable clinicians to make the best use and interpretation of laboratory studies and monitor therapeutic strategies, which consist mainly of administering supplements to restore body reserves.