Anemia, defined as hemoglobin level under lower normal limit, is a symptom of different pathologic conditions and the accurate differential diagnosis is necessary to determine the cause of anemia. The article uses the morphological classification of anemia to distinguish macrocytic, normocytic and microcytic types of anemias and divides anemias with increased amount of peripheral blood reticulocytes as a special group. It describes commonly known clinical units as iron deficiency anemia or anemia of chronic disease, as so as rare clinical units, which are always need to think about in a differential diagnosis of an anemic patient. There is an increasing incidence of rare blood disorders due to introduction of molecular genetics methods into diagnostics, prolonged overall survival of patients and increasing migration from areas with endemic occurrence of these diseases. Etiology, basic pathophysiological mechanisms, main clinical features together with important diagnostic examinations are described by each clinical unit. Due to the differential diagnostic focus of the article only basic knowledge about therapy is mentioned. The authors are members of the IHBT Center for Rare Disorders of Hematopoiesis, which is focused mainly on congenital and acquired disorders of red blood cell. Key words: anemia - differential diagnosis - enzymopathies - hemoglobinopathies - iron - macrocytosis - microcytosis - rare blood disorders - reticulocytosis.