Blue nevi may rarely appear in multiple form and grouped in a circumscribed area, a pattern of arrangement that is more properly designed under the term agminated blue nevi. In this paper a new case with light and ultrastructural studies is described, and the previously reported cases are reviewed. Histologically, there was a characteristic perifollicular arrangement of dermal melanocytes, most of which showed ultrastructurally an extracellular sheath. Agminated blue nevi seem to be benign lesions, but because of their rarity, no definite prognosis can be given.