Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 3 3 2009 09 15 34 36 Mohammadreza Ostadali Hematology- Oncology and Stem Cell Transplantation Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran Andisheh Ghashghaie Hematology- Oncology and Stem Cell Transplantation Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran Ardeshir Ghavamzadeh Hematology- Oncology and Stem Cell Transplantation Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran 2015 10 01 The most important factor in donor-recipient matching for hematopoietic stem cell transplantation is their HLA typing. For many patients, we can not find a full-matched donor. In high risk patients, one locus  mismatched related donors are suitable alternatives. (1, 2) Since the matching of patients and their siblings usually is based on low resolution HLA typing, the matching of one locus mismatched  siblings is always prone to catastrophic errors.   The following cases clearly demonstrate the possible pitfalls and highlight the importance of the HLA typing of parents in the matching of patients and their full-matched and one locus, mismatched siblings. https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/222 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/222/215