Purpose Nucleated cell dose is an important and modifiable factor in hematopoietic stem cell transplantation (HSCT), however its association with outcomes in the context of reduced intensity conditioning regimen (RIC) HSCT for adults with acute myelocytic leukemia (AML) is not known. Patients and Methods From 1998 to 2003, 253 patients with de novo AML, received transplants with RIC and peripheral blood from a genoidentical donor. Median age was 55 years (range, 18 to 72) and the median follow-up was 17 months (range, 2 to 67). One hundred forty one patients received transplants in first remission (CRI), 47 received transplants in second remission (CR2), and 65 patients received transplants in a more advanced phase. Fludarabin-based RIC was used in, 91%, of patients and low-dose (<4 Gy) total-body radiation in 23% of patients. The median nucleated and CD34 cell dose infused were 9.1 x 10(8)/kg and 5.8 x 10(6)/kg, respectively. Results,. Overall, 2-year leukemia-free survival (LFS) was 41% +/- 4% and it was 46% +/- 5% for patients receiving a higher cell dose (>9.1 x 10(8)/kg) and 37% +/- 5% for the remainders (P = .03). Higher cell doses exclusively benefited patients who received transplantations in CR2 or beyond, with LFS of 47 +/- 8 versus 20 +/- 8, with no detectable effect for patients who received transplants in CR1. In a multivariate analysis of the overall patient population, higher nucleated cell dose cells were associated with higher LFS (P = .04), higher incidence of chronic graft-versus-host disease (P = .01), and there was a trend towards a lower relapse incidence (P = .06). Interestingly, CD34+ cell dose was not associated with any outcomes. Conclusion Nucleated cell dose is an important factor that can be modified to improve results of RIC for patients with AML transplanted later than om CR1.