Alcohol causes different hematologic alterations on each of the three bone marrow cellular series. Its effect on the red series leads to the appearance of megaloblastic disturbances, erythroblastic vacuolization, iron metabolism abnormalities, and hemolytic syndromes. Megaloblastic disturbances may arise as a consequence of folic acid or vitamin B12 deficiency or of a direct toxic effect of ethanol on the erythroblasts. Iron metabolism alterations include reversible sideroblastic anemia, and hemosiderosis. The three hemolytic syndromes related to the consumption of ethanol are: acanthocytosis, stomatocytosis, and Zieve's syndrome. Alcohol induces leukopenia and functional deffects of the leukocytes; these facts explain the frequent susceptibility of chronic alcoholics to infection. Ethanol may act upon the megakaryocytic series to produce reversible thrombopenia and various alterations in platelet function. Thus alcohol exerts toxic effects on bone marrow, which interfere with the proliferation, maturation, release and survival of the three cellular series, either directly or by means of complex mechanisms related to the metabolism of folic acid, vitamin B12, pyridoxine, or iron. Alcoholism should therefore be considered as a possible cause whenever an obscure hematological condition comes under scrutiny.