[Atypical cellular blue nevus. Apropos of 1 case]

We report a new case of a cellular blue nevus with clinicopathologic atypia. It was a large lesion presenting clinically as a vascular tumor located in the middle of the back. It grew for 2 years without skin ulceration. The pathological study suggested a cellular blue nevus with moderate nuclear atypia, without any atypical mitosis and necrosis. The differential diagnosis such as malignant blue nevus and melanoma are discussed in search of a better definition of these rare lesions.