Mycosis fungoides (MF) is the most common subtype of primary cutaneous T cell lymphoma (CTCL). The erythrodermic form (T4) especially impairs health-related quality of life (HR-QoL), making patients often incapable of self-care. Mycosis fungoides and Sézary syndrome (SS) are immunogenic neoplasms and can be recognized by the patient's immune system. The disease is chronic and immunotherapy allows for long-term control of CTCL. The paper presents a description of 2 cases of nivolumab use in the salvage treatment of erythroderma in the course of refractory mycosis fungoides. Nivolumab was used as emergency treatment, and previously patients exhausted the available treatment options. The discussed cases confirm the effectiveness of immunotherapy in the treatment of primary cutaneous T cell lymphomas. The applied treatment achieved the effect of more than one year of response (15 months), as well as a significant benefit in terms of subjective and objective quality of life. The effect was mainly related to the condition of the skin. The use of the PD-1 checkpoint inhibitor allowed for over 12 months of control in advanced, refractory and heavily pretreated cutaneous lymphoma, and was very well tolerated. More research is needed on the use of such inhibitors in the treatment of cutaneous lymphomas.