Aim: To make doctors aware of the potential risk of developing melanocytic skin lesions and the possible development of malignant melanoma in patients chronically treated with adalimumab (Humira), a tumor necrosis factor-alpha (TNF-alpha) antagonist. Case report: A 38-year-old man came to the dermatology clinic because a month ago, he noticed the macroscopically visible change of the previously existing melanocytic lesion on the skin of the abdominal wall, in the form of enlargement and color change. Three years ago, the patient began to feel tightness in the thorax and back, morning low back pain and back pain, which would be reduced by taking non-steroidal anti-rheumatic drugs. Based on clinical, laboratory and radiological findings, the patient was diagnosed with axial spondyloarthritis, for which, two months later, adalimumab was introduced into his chronic therapy. The use of adalimumab led to a marked improvement in the patient’s condition, and he continued to take it regularly. After two years of continuous therapy with adalimumab, the patient noticed a change in the pre-existing nevus on his abdomen. He informed the dermatologist, who performed a total excision of the lesion. The pathohistological analysis confirmed a dysplastic nevus with a high degree of dysplasia. Conclusion: The association of adalimumab with melanoma development has not yet been sufficiently investigated, although much evidence supports this. Physicians must be aware of the possible risk of progression of pre-existing melanocytic lesions and the possible development of malignant melanoma, educate patients, and advise regular monitoring and caution to detect and prevent potentially serious side effects of adalimumab. Research on this topic is not numerous, and further studies are needed to consider several risk factors for melanoma.