Gemtuzumab ozogamicin (GO), a monoclonal antibody used in the treatment of acute myelogenous leukemia (AML) has been linked to the development of venoocclusive disease (VOD). We conducted a retrospective study of 62 patients with previously treated AML/MDS (myelodysplastic syndrome) who underwent allogeneic stem cell (SC) transplantation at our institution from December 2000 to October 2002 to determine whether GO exposure prior to allogeneic SC transplantation increases the risk of developing VOD. Fourteen patients received GO prior to SC transplantation. Of 62 patients, 13 (21%) developed VOD; 9 (64%) of 14 with prior GO exposure developed VOD compared with 4 (8%) of 48 without prior GO exposure (P <.0001). Logistic regression controlling for sex, disease status, donor type, and graft-versus-host disease prophylaxis identified prior treatment with GO as a significant risk factor for VOD (odds ratio [OR], 21.6; 95% confidence interval [CI], 4.2-112.2]. Nine of 10 patients who underwent SC transplantation 3.5 months or less following GO developed VOD compared with none of 4 patients who underwent SC transplantation more than 3.5 months from GO administration. Three of 14 patients who received GO prior to SC transplantation died of VOD. We conclude that patients undergoing SC transplantation within a short interval from GO administration are at increased risk of developing VOD.