Mucosal melanoma, or so-called mucosal-oral melanoma is a rare but serious diagnostic and therapeutic problem. The "primary mixed" mucocutaneous forms of melanoma, which affect both the mucosa and the adjacent skin, are also particularly problematic and rare. Given that the staging, diagnosis, and treatment of mucosal (oral) melanoma differs from that of cutaneous melanoma, staging in mixed melanoma (primary mucocutaneous melanoma) as well as decisions for each subsequent diagnostic and therapeutic step should be individualized and modified according to the recommendations of the respective two classifications (for cutaneous but also mucosal melanomas), while at the same time or at least to a large extent overlapping with them. In practice, the following paradoxes occur during staging - there are melanomas with the same tumor thickness, but in different stages, which should be treated in a different, consensus-based way. At the same time, it would be appropriate for the surgical interventions to be in accordance with the patient's wishes for minimal trauma/reduced risk of developing facial disproportion. We present the case of a 69-year-old patient with a newly-developed lesion in the area of the mucosa of the upper lip and adjacent skin, which was identified as a primary mucocutaneous form of melanoma after surgical removal. The complex pathogenesis of the disease is discussed herein, emphasizing the role of UV radiation, iatrogenic immunosuppression with mycophenolate mofetil, tacrolimus, and prednisolone (due to severe glomerulonephritis leading to kidney transplantation), as well as the potential possible but speculative pathogenetic role of acetyl salicylic acid, etc. Primary mucosal and mucocutaneous forms of melanoma remain a challenge for clinicians, and steps for their diagnosis and treatment should be an expression of multidisciplinary, consensual solutions.