The purpose of the study was to compare two different quality-of-life self-rating instruments, namely the EORTC QLQ-C30, developed by the quality-of-life study group of the European Organisation for Research and Treatment of Cancer, and the FACT-BMT (version 3), the Functional Assessment of Cancer Therapy - Bone Marrow Transplantation scale, which is the FACT-G(eneral measure) in combination with a module developed specifically for evaluating quality of life of bone marrow transplant (BMT) patients. Fifty-six BMT recipients completed both the EORTC QLQ-C30 and the FACT-BMT (German language version) during the same session. Questionnaire data were analyzed on a subscale basis using correlation analysis and multiple linear regression. Correlations between corresponding subscales of EORTC QLQ-C30 and the FACT-BMT ranged from r=0.30 for the emotional domain (poor agreement) to r=0.77 for global QOL (good agreement). This suggests that the instruments, despite considerable overlap, possibly focus on different aspects of QOL, in particular in addressing emotional and social issues of BMT patients. It appears that the FACT-BMT gives a more comprehensive overview regarding the multidimensional construct of quality of life. The EORTC QLQ-C30 gives more insight into the physical aspects of quality of life and helps to identify symptoms which effectively decrease quality of life from the patient's perspective. The QLQ-C30 might be improved by the incorporation of a BMT-specific module currently under development. We therefore conclude that neither of the two instruments can be replaced by the other in the assessment of QOL of BMT patients and that a direct comparison of results obtained with the two instruments is likely to be misleading.