Pilomatricoma (calcifying epithelioma) is a benign tumor of the hair m
atrix cells that presents most frequently in childhood. Most are benig
n and slow growing and do not recur after excision. A small number of
aggressive or malignant variants have been reported that recur if not
widely excised. We report on an aggressive variant occurring in a 4-ye
ar-old boy and advise caution in treating cutaneous ''cysts.''