Histone deacetylase inhibitors such as vorinostat enhance gemtuzumab ozogamicin efficacy in vitro. We, therefore, investigated vorinostat+gemtuzumab ozogamicin for adults aged 60 years and over with untreated acute myeloid leukemia. We stratified patients into 2 groups (group 1: patients aged ≥ 70 years and performance status 2-3; group 2: aged 60-69 years with performance status 0-3 or aged ≥ 70 years and performance status 0-1). Responses were monitored separately in group 2 patients with normal or favorable cytogenetics (group 2A) and other cytogenetics (group 2B). Among 31 patients, 6 (19.4%) achieved complete remission, and one (3.2%) achieved complete remission with incomplete platelet recovery; these patients had a higher median overall survival than non-responders (553 vs. 131 days, P = 0.0026). Response rates were: group 1, one of 10 (10.0%); group 2A, 6 of 13 (46.2%); and group 2B, none of 8 (0%). These data indicate that vorinostat+gemtuzumab ozogamicin has activity that is mostly confined to patients with normal karyotype disease. ClinicalTrial.gov: NCT00673153.