Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) contributes to the recruitment of donor T cells into the mucosal tissues of the recipient after allogeneic hematopoietic stem cell transplantation (aHSCT). The aim of our study was to determine whether selected single nucleotide polymorphisms (SNPs) of the MADCAM1 gene are associated with development of serious complications after aHSCT.