[Diagnosis of malignant blue nevus]

A case of malignant melanoma of the femur is described. The tumor has arisen in the presence of proliferating blue nervus. Differential diagnosis appeared complicated due to a high degree of cell differentiation in apparent anaplasia of the tumor tissue. Malignant nature of the process was evident from a rapid proliferation of the long-standing pigmented new growth, its large size, necrosis and mitoses presentation.