Blue nevus is an uncommon pigmented lesion of dermal melanocytes. By convention, two well defined histologic variants, designated as "common" and "cellular", have been recognised. In the last few years, these lesions have attracted much attention due to the recognition of news entities and to its confusion with malignant melanoma. In the present review, we point out the more striking features of new related entities (combined nevus, deep penetrating nevus, compound blue nevus) and establish the differential diagnosis with conflictive lesions such as atypical blue nevus, locally aggressive blue nevus, congenital giant melanocytic nevus with nodular growth and melanocytic dermal tumor of unpredictable outcome. We also review the concept of malignant blue nevus and the significance of lymph node metastases. The blue nevus is an uncommon pigmented lesion consisting of dermal melanocytes that can appear in diverse forms: dendritic, spindle-shaped, oval-shaped, or polyhedral. Although it usually occurs in skin, it has been reported in other locations, such as oral mucosa, sclera, uterine cervix, vagina, prostate, spermatic cord, pulmonary hilus, orbit, conjunctiva, maxillary sinus, breast, and lymph nodes 3,8,42,49. Generally, it occurs in adults as a single, acquired, intensely pigmented lesion, although familial and multiple nevi have been reported 7,39. By convention, there are two well-defined histologic variants, designated as "common" and "cellular", but lesions often manifest intermediate features. In the last few years, blue nevus has attracted much attention due to the recognition of new (clinical and histologic) entities and to its confusion with malignant melanoma.(ABSTRACT TRUNCATED AT 250 WORDS)