The cytokine G-CSF stimulates myeloid progenitors and is routinely used to accelerate neutrophil recovery in the treatment of hematological malignancy and blood or marrow transplantation. Despite significant reductions in the frequency and duration of febrile neutropenia episodes, infections and the length of hospitalization, filgrastim has never been conclusively proven to produce a survival benefit in allogeneic HSCT and is considered a supportive measure. In this review, we analyze the conflicting evidence and appraise the utility of G-CSF in allogeneic HSCT. G-CSF administration after allogeneic HSCT needs to take into consideration the impact on immune reconstitution, risk of leukemic progression in patients with chromosome 7 abnormalities and the absence of proven benefit in patients receiving marrow or peripheral blood progenitors as the stem cell source.