The hematological status of 81 infants with Down syndrome was reviewed retrospectively. Twenty babies had no hematological evaluation, 33 had a normal hematological status, and 28 had at least one abnormality, either of hematocrit, white cell count, or platelet count. Among these were 18 babies with increased hematocrit, one with decreased hematocrit, four with decreased platelet count, one with increased white cell count, three with increased hematocrit and decreased platelet count, and one with increased platelet count and increased white cell count. Some of these babies were evaluated for neoplasia or sepsis; however, in all the abnormal blood findings disappeared by 3 weeks without evidence of malignancy or infection. We conclude that hematological abnormalities with a benign natural history are common in Down syndrome infants.