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Since the treatment for mucosal melanoma often accompanies surgical difficulty, carbon-ion radiotherapy in combination with immune check point inhibitors (ICI) against programmed cell death 1(PD-1) and/or cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is a favorable choice. Radiation recall henomenon (RRP) is represented by an inflammatory reaction within previously irradiated fields,such as mucositis, dermatitis, and pneumonitis, in association with the administration of chemotherapeutic agents.1 Here, we report a case of carbon-ion radiation recall mucositis associated with nivolumab and pembrolizumab for melanoma located in the paranasal sinuses. A 71-year-old Japanese woman was referred to us because of cheek pain and bloody rhinorrhea. Computed tomography revealed a tumor in the left paranasal sinuses without metastasis.Histopathological examinations showed that atypical cells proliferated in the mucosa (Figure 1a). The tumor cells were positive for Melan-A and HMB-45 (Figure 1b), consistent with mucosal melanoma. As the tumor was unresectable, it was treated with carbon-ion radiotherapy (Figure 1c), and local resolution was achieved. However, bilateral adrenal metastases were observed 1 year later without local recurrence,and then nivolumab as anti-PD-1 antibody was administrated. At 1 week after the first administration of nivolumab, the patient complained of left oral pain. Physical examination revealed erythema and swelling on the left upper lip (Figure 1d), and erosive ulcers on the left side of the palatal, buccal, and nasal mucosa (Figure 1e), although histopathological examination was not performed in accordance with the patient’s wishes. The symptoms were resolved by discontinuation of nivolumab. Despite the change from nivolumab to pembrolizumab as another anti-PD-1 antibody, mucositis recurred 1 week after the administration of pembrolizumab (Figure 1f). We diagnosed the patient as radiation recall mucositis associated with anti-PD-1 therapy, s