Erythrodermic psoriasis is a severe form of psoriasis, presenting as prominent erythema, affecting the whole body. Ustekinumab (Stelara®) is a human monoclonal antibody targeting the p40 subunit shared by interleukin IL-12 and IL-23. Erythrodermic psoriasis has been an exclusion criteria in studies looking at the efficacy of ustekinumab against psoriasis, but recently, a few reports have proven its efficacy on erythrodermic psoriasis. Herein, we report 2 cases of erythrodermic psoriasis that successfully improved with ustekinumab. A 42-year-old man presented with a 7-year history of erythrodermic psoriasis and psoriatic arthritis. The patient was treated with ustekinumab 45 mg subcutaneously at 0, week 4, and every 12 weeks thereafter. At week 28, his Psoriasis Areaand Severity Index (PASI) score decreased from 64.8 to 9.6. The second case is a 26-year-old man suffering from erythrodermic psoriasis for 10 years. Four months after the first administration of ustekinumab, the patient achieved 75% improvement of the PASI score and 90% improvement after 112 weeks. Although further studies are required, it is likely that ustekinumab can be an effective therapeutic option for patients affected by erythrodermic psoriasis.