Xeroderma pigmentosum (XP) is a rare genodermatosis characterized by a defect in the repair of DNA damage induced by ultraviolet rays. The cutaneous tumours are frequent and occur at an early age, but neoplasias of the mucosae are seldom observed. Among the mucosae, the lipids and the conjunctiva clearly predominate. Tumours of the buccal cavity are much less frequent, and this is why we report a case of epidermoid carcinoma of the tip of the tongue in a Moroccan boy. Only 25 cases of intrabuccal tumour have been reported in patients with XP, and 22 were epidermoid carcinomas of the tip of the tongue. These carcinomas may be preceded by precancerous lesions such as leucoplasia. The early occurrence and elective location at the tip of the tongue clearly differentiate lingual carcinomas associated with XP from their homologues in adults. The aggressiveness of these lesions is difficult to determine due to a usually short follow-up and to the lack of details in reports. Treatment is surgical and non-specific. Concerning epidemiology, the predominance of African and Near-Eastern patients among those suffering from lingual carcinoma is striking. Moreover, when the complementation group is known it is always group C; our patients presented with characteristics of this group. Some authors believe that the lingual tumours are due to ultraviolet light (overexposure in case of natural pigmentation, with exposure of the tip of the tongue) and to certain toxic substances in food.(ABSTRACT TRUNCATED AT 250 WORDS)