Pigmented naevi (melanocytic naevi) are common and are widely distributed all over the body. The average number of naevi seen in a Caucasian is between twenty and thirty. They are either congenital or acquired benign neoplasm of melanocytes. They may occur as giant lesions at birth, and are more prone to malignant transformation. However, the risk of malignant transformation associated with naevi irrespective of size is well established and a variety of malignancies have been reported to arise from a naevus. The incidence of malignant transformation in naevi is 4% to 9%. We present two cases of malignant tumours arising from pre-existing naevus. The first was a 60-year old woman with a malignant melanoma arising in a vulva intradermal naevus. The second was a 51-year old woman with a basal cell carcinoma arising in a facial naevus.