An optimistic attitude is hypothesized to be beneficial when facing a life-threatening medical condition. However, the actual relationship of high expectations for treatment success and medical outcome is controversial. Using a prospective cohort of 313 autologous and allogeneic hematopoietic stem cell transplant patients enrolled July 1996 through November 1999, we tested whether patient-reported expectations before transplantation were associated with survival and quality of life following the procedure. Before transplantation, patients with higher expectations that the transplant procedure would go well had better mental and emotional functioning, but similar physical status and medical condition to patients with less optimistic expectations. In the first 2 months after transplantation, optimistic expectations were associated with better survival (92% v 84%; relative risk for mortality 0.45, 95% confidence interval 0.22-0.92; P=.03) controlling for other physical and mental characteristics. However, by 6 months posttransplantation, survival and quality of life were indistinguishable between patients with initially higher and lower expectations. Our data suggest an association between more optimistic expectations and early survival following hematopoietic stem cell transplantation, but this association is not present by 6 months posttransplantation.