It is well known that patients undergoing allogeneic haematopoietic stem cell transplantation (HSCT) experience changes in quality of life. We investigated factors associated with quality of life changes in adult HSCT patients. The Functional Assessment of Cancer Therapy - Bone Marrow Transplantation (FACT-BMT) scale, supplemented with the Functional Assessment of Chronic Illness Therapy - Spiritual Well-being (FACIT-Sp) subscale, was administered on three occasions, immediately before transplantation, 100 days and 12 months after transplantation. Analyses of nine selected factors were made where changes in quality of life were found. Seventy-five patients were included and 40 of these completed the study. Emotional well-being was found to improve between the baseline and 100 days, while all other dimensions deteriorated, including overall quality of life. Physical and social/family well-being deteriorated between the baseline and the 12-month follow-up, while emotional well-being improved. The main factors associated with deteriorating quality of life over time were found to be significant infections, female gender and transplantation with stem cells from a sibling donor. In our further studies we aim to focus on the relationships between patients and sibling donors in order to improve the care. Careful attention must be paid to continuous adequate information during the transplantation procedure.