A man born with a unilateral epidermal naevus on the right side of the abdomen developed at puberty symmetrical benign acanthosis nigricans in the body folds. Tbe symmetrical eruption later disappeared completely. Tbe unilateral epidermal naevus and tbe symmetrical eruption showed identical bistological features, i.e. tbose of acantbosis nigricans. At tbe age of 32 be developed a muco‐epidermoid cancer of the left parotid gland. A decision wbetber tbe association of unilateral epidermal naevi witb malignant tumours occurs witb unusual frequency requires (a) a long follow‐up of the patient with the unilateral naevus, (b) a differentiation of the unilateral eruption from unilateral malignant acan‐thosis nigricans and (c) statistical evidence.