Transplantation with unrelated donor (UD) marrow has been shown to potentially cure patients with leukemia. Between January 1991 and April 1998, 54 patients with leukemia have received an UD BMT at our institution. Five patients received their UD BMT as a second transplant after a preceding autologous or syngeneic BMT and were excluded from further analysis. Forty-nine patients with leukemia (acute leukemia n = 26; CML n = 23) and a median age of 36 years (range 19-51) were analyzed. For conditioning, all patients received a combination of fractionated TBI and CY. GVHD prophylaxis consisted of MTX and CsA in all patients. As of 30 April 1998, 27 of 49 (55%) patients survive after a median observation time of 18 months. The probability of overall survival for standard risk and high risk patients is 54% and 31% (P = 0.05). Probability of transplant-related mortality (TRM) is 27%, 24% in standard risk and 31% in high risk patients (P = 0.44). Patients younger than 40 years (n = 33) had a similar TRM as patients 40 years and older (n = 16). The probability of relapse is 41% for the whole group, 29% for standard risk and 55% for high risk pts (P<0.05). Our data confirm that UD BMT is an effective treatment for patients with leukemia. TRM is almost similar to related sibling BMT, most probably due to improvements in HLA typing technology, conditioning regimen and supportive patient care.