The causes of megaloblastic anemia were studied in a survey of patients admitted to six Israeli hospitals over a period of 15 yr. Among the 203 patients identified, 69% had pernicious anemia, 12% had gastrointestinal disease, 9% had primary nutritional deficiency of whom only 1% were associated with pregnancy, and 7% had selective vitamin B12 malabsorption with albuminuria. Comparison with previously published surveys showed, that in contrast with earlier studies where primary nutritional deficiency was the cause of megaloblastic anemia in about 70% of cases and pernicious anemia in only 20%, in more recent studies the proportion of cases with primary nutritional anemia in general and those associated with pregnancy in particular was much lower. This is most probably the result of improved standards of living and a national program of preventive folate supplementation at maternity clinics. A potential hazard of such preventive programs is the aggravation of neurological complications in patients with undiagnosed vitamin B12 deficiency. Early recognition of pernicious anemia and other forms of selective B12 malabsorption is a new challenge created by the changing pattern of megaloblastic anemias.