This meeting was convened by Richard T. Silver and co-chaired by Jerry L. Spivak. It was held from 27 to 29 October 2005 in Washington, DC. Thirty-one invited speakers from seven different countries participated in the conference, which was attended by more than 300 individuals from 23 countries. As in previous years, a clinical symposium for patients, held the day before the symposium, was sponsored by the Cancer Research and Treatment Fund, Inc., New York, NY 10021. This meeting report provides a summary of the five sessions prepared and highlighted by one of the session chairs. In addition to the formal presentations on the biology, clinical aspects and management of these diverse marrow stem cell disorders, there was considerable interest generated because of the availability of several new agents that have been recently approved. A special luncheon satellite symposium was devoted to the dramatic changes in the therapeutic options for the myelodysplastic syndromes, sponsored by MGI Pharma, Inc. The keynote address was presented by Dr. George Q. Daley from Harvard Medical School and the Children's Hospital Medical Center. He reviewed the molecular steps in the formation of the Philadelphia chromosome and some of the newly described mutations leading to resistance to chemotherapy (see Section 4).