The records were reviewed of 58 patients receiving transplants in Seattle with unmanipulated marrow from HLA-identical siblings during the accelerated phase (AP) of chronic myeloid leukemia. Variables examined for association with survival and relapse included the interval from diagnosis to transplant, the reasons for categorization as AP, age, regimen, and cytomegalovirus serology. Four patients relapsed. The 4-year probabilities of survival, relapse-free survival, nonrelapse mortality, and relapse were 0.49, 0.43, 0.51, and 0.12, respectively. After completion of the stepwise multivariate analysis, age less than 38 years and categorization as AP solely on the basis of chromosomal abnormalities emerged as being independently significantly associated with improved survival. The 4-year probability of survival for the 16 patients categorized as AP because of chromosomal abnormalities and receiving transplant less than 1 year from diagnosis was 0.74. The low probability of relapse in these patients suggests that more aggressive preparative regimens are not indicated for patients receiving transplants in AP because of the increased risk of transplant-related mortality.