On the suspicion that folate deficiency was not being thoroughly investigated we conducted a retrospective study of management in a teaching hospital. Notes from 84 consecutive patients with low red cell folates (mean age 69.5 years, range 21-95, M:F 33:51) were reviewed for haemoglobin, mean cell volume, dietary history, alcohol consumption, drug history, relevant medical history, relevant investigations, treatment, repeat measurement of red cell folate and diagnosis of deficiency. In 52 (61.9%, mean age 72.9 years, range 33-95, M:F 21:51) no diagnosis was reached. In only 32 (38.1%, mean age 63.9 years, range 21-89, M:F 12:20) was a definitive diagnosis established: 5 had coeliac disease, 1 had Crohn's disease, 9 had drug-associated deficiency (4 methotrexate, 3 phenytoin, 1 trimethoprim and 1 valproate), 1 had combined variable immunodeficiency and 16 had dietary deficiency. In most cases of folic acid deficiency no attempt was made to establish aetiology. We recommend that younger patients without an obvious cause are investigated initially by dietary assessment and measurement of anti-endomysial antibody and by duodenal biopsy with small-bowel follow-through if clinically indicated.