SUMMARY.— The clinical records and the histopathology of 140 cases of naevus sebaceus and related compound epidermal naevi have been studied with special reference to the incidence of secondary tumours. In 27 lesions there were areas of syringocystadenoma papilliferum, sometimes forming a large part of the naevus. In 9 lesions, basal cell epithelioma was a secondary development, but only 3 of these epitheliomata showed evidence of an aggressive growth pattern. Fourteen other naevi were found histologically to have small areas of basaloid proliferation, but these proliferations were considered to be harnartomatous rather than epitheliomatous in nature. So far, on follow‐up, none of the basal cell epitheliomata has recurred after treatment.
A rare complication found in a patient aged 56 was the development of a squamous cell epithelioma which, although poorly differentiated, had not recurred 4 years after excision. Other related lesions were 3 syringomata, 2 apocrine cystadenomata and 2 osteomata. Some of the naevi showed areas of unusual squamous proliferation which were difficult to categorize histologically; in 2 instances keratoacanthomata were simulated; other proliferations showed “clear cell” differentiation or pseudo‐epitheliomatous hyperplasia. It was concluded from this study that there is only a small risk of a serious malignant tumour supervening in naevus sebaceus, and that simple surgical excision is usually adequate treatment.