ITF2357, an orally effective member of the family of histone deacetylase inhibitors, is a potent inducer of apoptosis and death of multiple myeloma (MM) cells. We performed a phase-II, multiple-dose clinical trial in 19 patients with relapsed or progressive MM to determine the maximum tolerated dose (MTD) of ITF2357 administered twice daily for four consecutive days every week for 4 weeks (i.e., first cycle). The first six patients received 150 mg ITF2357 twice daily. Since two of them experienced a dose-limiting toxicity (DLT) during the first cycle, the subsequent patients received 100 mg ITF2357 twice daily. This was the MTD, as only one DLT occurred. Up to 12 weeks (i.e., three cycles) of treatment were scheduled. Oral dexamethasone was allowed to a maximum weekly amount of 20 mg. Median duration of treatment was 6 weeks, ranging from two (two patients) to 12 weeks (five patients). Four patients suffered from serious adverse events. Three patients experienced grade 3-4 gastro-intestinal toxicity and three had transient electrocardiographic abnormalities. Thrombocytopenia occurred in all but one patient (grade 3-4 in ten patients). At last follow-up, five patients were in stable disease, five had disease progression, and nine had died all of progressive MM. In conclusion, when given at a dose of 100 mg twice daily alone or combined with dexamethasone, ITF2357 proved tolerable but showed a modest clinical benefit in advanced MM.