Outcome of patients with myelodysplastic syndrome after azacitidine failure is poor. In this population, we combined cytarabine (10-20mg/m2/day 14 days) with vorinostat (400mg/day) for escalating durations (7 days, 10 days and 14 days), and starting on day 1 (concomitant arm) or on day 14 (sequential arm) following a 3+3 phase I design. 40 patients were treated. Dose limiting toxicities were all seen in sequential arm. The overall response rate was 15% with 4 responses in concomitant arm (ORR=25%). We conclude that this combination is tolerable and concomitant administration might be less toxic and have better therapeutic effect (clinicaltrials.gov NCT00776503).