Background:Cellular combinations in the same neoplasm can have intriguing physiopathological implications, which may be useful to better understand the biology of the diseases.Main observations:Urticaria pigmentosa in association with eruptive melanocytic nevi was observed in a female patient. Maculopapular lesions extended at the base of different melanocytic nevi and the histopathological examination revealed the presence of a mast cell population in the papillary and reticular dermis combined with overlying melanocytic nevi. The re-evaluation of a melanoma removed three years before revealed the presence of the same pathological features. Immunohistochemical assays showed a strong positivity to Giemsa, Toluidine blue and CD-117 in the mast cells, while a S-100 reaction was observed in the melanocytic population.Conclusions:We discuss possible pathogenetic linkage between cutaneous mastocytosis and melanoma.