Large or giant cellular blue nevi are usually congenital and represent a challenge for the physician. Close anatomic structures may be altered by the size of the moles. In this article, we report the case of an uncommon large, agminated, cellular blue nevus of the 'plaque type' in a 42-year-old female. Due to the risks of malignant melanoma development on a large or giant blue nevus, we highlight the importance of proper histopathological diagnosis. Furthermore, because of the possibility that the nevus may invade the bone and cerebral tissues, we discuss the indication of a radiological diagnosis. The accurate correlation to clinical and histopathological findings and appropriate multidisciplinary management can save the lives of patients.