Bloom syndrome is a genomic instability syndrome associated with predisposition to development of various types of malignancy. In this report, rye described a 7-year-old boy with Bloom syndrome (BS) and myelodysplastic syndrome (MDS) associated with monosomy 7 and loss of the Y chromosome. To our knowledge, this was the first case with BS showing monosomy 7 and MDS during the early childhood period. (C) 1999 Elsevier Science Inc., 1999. All rights reserved.