Ninety-three patients with myelodysplastic syndrome with either excess blasts or life-threatening cytopenia received cyclophosphamide and total body irradiation (88 patients) or busulfan (5 patients) followed by allogeneic (90 patients) or syngeneic (3 patients) marrow infusion. Thirty-eight patients are disease-free survivors between 1.8 and 11.3 years (median 6.1 years) after transplantation. The median Karnofsky performance status of the survivors is 100%, and only 2 have a performance status of < 80%. Eighteen patients relapsed and the remaining 37 died without evidence for relapse. The 5-year actuarial disease-free survival, relapse, and non-relapse mortality rates are 40%, 29%, and 44%, respectively. The actuarial relapse rate was higher among patients with excess blasts at the time of transplantation compared to those without excess blasts (49% vs. 4%, p = 0.0001), resulting in a lower disease-free survival (31% vs. 54%, p = 0.07). Increasing age was associated with a lower disease-free survival (p = 0.02). In a multivariate analysis, younger age, shorter disease duration, and absence of excess blasts were associated with improved outcome. We recommend that patients with myelodysplasia with appropriate marrow donors, especially patients less than age 40, undergo marrow transplantation early during the disease course, before the disease progresses or life-threatening complications develop.