We report two cases of adult acute lymphoblastic leukemia presenting with preleukemic phase of pancytopenia with a few abnormal lymphoid cells in bone marrow aspirates. The initial diagnosis of each case was suspicious aplastic anemia and hypoplastic anemia. Both cases progressed to overt acute lymphoblastic leukemia within 1 year. We suggest that initial pancytopenic phase (pre-ALL) may precede the diagnosis of acute lymphoblastic leukemia in adults and differential diagnosis from myelodysplastic syndrome and primary aplastic anemia will be needed. We also suggest that primary bone marrow lymphoma and "primary unknown metastatic lymphoma of bone marrow" may be possible as the pathogenesis in a case like ours.