A standardized treatment for patients with relapsed APL has not yet been established. With arsenic trioxide (ATO) monotherapy remission rates over 80% were achieved and long-lasting molecular remissions are described. The drug was mostly well tolerated. ATO exerts a dose dependent dual effect on APL blasts, apoptosis in higher and partial differentiation in lower concentrations. ATO was also successfully administered before allogeneic and autologous transplantation. ATO is approved for the treatment of relapsed and refractory APL in Europe and in the USA.