Mobilized peripheral blood has replaced the use of bone marrow as a source of hematopoietic stem cells in most autologous transplants and is increasingly used in allogeneic transplants. The hematopoietic reconstitution after using mobilized peripheral blood is faster compared to bone marrow. Umbilical cord blood has emerged as another rich source of hematopoietic stem cells for transplantation. The minimal risk to the donor and the rapid availability are among the great advantages of this stem cell source. The slow recovery of neutrophil and platelet counts is the major clinical concern. Bone marrow biopsy is an important tool for obtaining information regarding the hematopoietic recovery after hematopoietic stem cell transplantation. The histopathological hematopoietic reconstitution of the bone marrow after umbilical cord blood transplantation is delayed compared to bone marrow transplantation. 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