The objective of this review was to evaluate oral cobalamin (vitamin B(12)) therapy in adult and elderly patients, from the perspective of a hematologist. PubMed was systematically searched for English and French articles published from January 1990 to January 2007. Data from our working group, the 'Groupe d'étude des carences en vitamine B(12)des Hôpitaux Universitaires de Strasbourg', have also been included. Several prospective studies in well-determined population (n = 4), prospective randomized studies (n = 3) and a systematic review by the Cochrane group (n = 1) provide evidence that oral cobalamin therapy may adequately treat cobalamin deficiency, particularly hematological abnormalities or manifestations. These studies suggest that at least 1000 microg/day of oral cyanocobalmin are needed for pernicious anemia and a mean daily dose of 250 microg for food-cobalamin malabsorption. This present review confirms the previously reported efficacy of oral cobalamin treatment in adult and elderly patients.