Arsenic trioxide (ATO) has been proposed as an option for the treatment of relapsing or refractory multiple myeloma. In order to critically appraise the published clinical evidence, a systematic search of the databases PubMed, Embase, Web of Science and the Cochrane Library was performed. Studies were selected according to prospectively defined criteria. Eventually 16 articles met the inclusion criteria. Six trials evaluated ATO as a single agent or in combination with ascorbic acid and ten trials added ATO to other cytostatic agents. Apart from one randomized controlled trial (RCT), all other studies were designed as case series. The patient numbers were generally small, treatment regimens differed both regarding the dosage of ATO and combinations with other drugs. Monotherapy with ATO resulted in partial response rates between 0% and 17% and minimal responses of 7-33%, resulting in mean overall response rates of 30%. Overall response rates in combined regimens varied widely between 12% and 100%. Response rates for patients in the three arms of the RCT did not differ significantly. The results demonstrate the potential efficacy of ATO in refractory multiple myeloma, but the validity of these findings is reduced by considerable methodological flaws. RCTs should further investigate the efficacy of ATO or new arsenicals in order to overcome methodological concerns of the studies presented here. With respect to the higher evidence level of new substances such as bortezomib or lenalidomide, at present ATO has no role in routine management of relapsed or refractory myeloma.