Pre-transplant characteristics of 137 consecutive patients (including 103 patients with one or more features suggesting advanced disease) undergoing related donor marrow transplant for chronic myeloid leukemia (CML) were analyzed to determine their association with outcome. Multivariate analysis identified increased recipient age (relative risk (RR) for patients over 30 years of relapse or death 2.37; P = 0.004), and longer interval between diagnosis and transplant (RR 1.20; P = 0.0001) as significant adverse influences on disease-free survival (DFS). The 5-year DFS for patients transplanted within 1 year of diagnosis (¿early transplant', n = 71) was significantly higher (51%) than that for patients transplanted beyond 1 year from diagnosis ('delayed transplant', n = 55) (34%; log rank P = 0.02). For early transplant patients, poor prognostic features included myelofibrosis (RR 3.53; P = 0.018), splenomegaly (RR 2.22; P = 0.029) and the use of a female donor (RR 3.16; P = 0.002). The 5-year DFS for patients transplanted within 1 year of diagnosis and without signs of advanced disease was 67%. The presence of increasing numbers of features suggesting acceleration prior to transplant had a cumulative adverse influence of DFS. The risk of relapse (5 year estimate 20%) was also independently and significantly increased in association with a longer interval from diagnosis to transplant (P = 0.012). Early transplant is an important influence on DFS and relapse after related donor transplant therapy for CML, although additional patient characteristics influencing outcome can be identified and may have cumulative adverse effects.