Background: Development of a second primary melanoma (SCPM) has not been reported in melanoma patients treated with anti-PD-1 monoclonal antibodies (mAb), in contrast with those reported in BRAF-inhibitor-treated patients. Our aim was to report arising SCPM in patients with advanced melanoma treated with anti-PD-1 therapy. Methods: Retrospective study, conducted in 2 referral centres, including advanced melanoma patients who developed a SCPM after anti-PD-1 mAb initiation, between September 2010 and May 2019. BRAF or NRAS mutational status was assessed by targeted NGS panels, real-time PCR, and immunohistochemistry. Results: Among a total of 509 patients treated with anti-PD-1 mAb, 4 had a SCPM (incidence: 0.8%; 95%CI: 0.02-1.57%). All patients were treated with nivolumab, in first (N = 3) or second line after progression with BRAF + MEK inhibitors (N = 1). No immune-related adverse event greater than grade 2 according to Common Terminology Criteria for Adverse Events version 5.0. was observed in these 4 cases; a vitiligo-like depigmentation (grade 1) was observed in two patients. The median time from the first nivolumab infusion to the SCPM diagnosis was 17.5 months (range: 5-21). All patients developed the SCPM after achieving a complete response. Nivolumab administration had been discontinued (4 months prior) in one patient. Histology revealed 4 superficial spreading melanomas (SSM): one invasive (without BRAF^V600 mutation) and 3 intraepidermal melanomas (2 with a BRAF^V600E mutation and one with a NRAS^Q61H mutation). 3 patients had risk factors for developing multiple melanomas: a dysplastic nevus syndrome, a high number of nevi (≥100 nevi), and a family history of melanoma in first-degree relatives and constitutional heterozygous mutation of exon 2 of the CDKN2A gene. Occurrence of SPCM did not alter advanced melanoma treatment. With a median follow-up of 29 months [range: 18-41] from the first anti-PD-1 mAb infusion, all patients had prolonged CR, and treatment was discontinued in all patients, without relapse after a median 11.5 months [0-18] off therapy. The median duration of nivolumab treatment was 15.5 months [10-24]. Conclusions: Although anti-PD-1 mAb could theoretically decrease the risk of developing another melanoma in metastatic melanoma patients, we found 4 such cases, highlighting the importance of regular clinical screenings for new primary melanoma in patients with metastatic melanoma even when responsive to anti-PD-1 therapy. Immune checkpoint inhibitors do not totally prevent the risk of occurrence a SCPM.