Emerging literature suggests that quality of life (QOL) after bone marrow transplantation is relatively good but is accompanied in some patients by a variety of residual difficulties. The studies supporting this finding, however, have been somewhat limited in scale, scope, design, and analysis. We comprehensively measured changes in multidimensional QOL in a 4-year longitudinal follow-up of 415 adult patients who received hematopoietic stem cell transplants at Fred Hutchinson Cancer Research Center. Questionnaire packets containing 271 items were mailed annually posttransplantation to patients' homes. Standard methods of analysis yielded conditional estimates depending on compliance and survival, whereas new, likelihood-based methods generated unconditional estimates applicable to the full intent-to-treat population. Typical QOL levels generally remained high over the entire study period. Most QOL functioning significantly improved over 4 years, with the remainder showing no important decrement. Although isolated problem areas, such as sexual dissatisfaction, did emerge, the level of dysfunction for most physical and psychological scales remained below 30% of scale maxima. Broadly similar results were obtained for conditional estimation, which may contain an optimistic bias, and for unconditional estimation, which largely avoids the bias. Because concurrence was obtained between the 2 types of estimation, we conclude that most patients really do experience good levels of QOL in the 4 years after transplantation. Although some problems can be anticipated, typical patients can look forward to a QOL after transplantation that is broadly comparable to that of the normal population. Biol Blood Marrow Transplant 2000;6(5A):576-91.