Melanocytic tumors are one of the major problems in diagnostic dermatopathology as they comprise benign nevi, malignant melanomas and borderline cases. Apart from a proportion of congenital lesions, most benign nevi are acquired tumors that arise during early adulthood and eventually may undergo regressive change. Histologically, they present as so-called common nevi, so-called dysplastic nevi, Spitz's nevi, blue nevi and their variants, and combined nevi. In typical cases, the distinction from a malignant melanoma is not difficult. However, benign simulators of malignancy exist as much as deceptively bland appearing melanomas and in some cases the diagnosis remains dubious despite careful weighting of criteria. Indeed, morphological features may not always suffice to disclose the nature of a melanocytic tumor. Ancillary techniques including immunohistochemistry and measurement of telomerase activity may be of assistance in this respect. One should nevertheless be aware that the biological behavior of certain borderline cases cannot be predicted with certainty.