Cowden syndrome is a multisystemic cancer predisposition disorder, in which the mucocutaneous lesions are the most constant features. We present a case of Cowden syndrome in a teenage boy with hyperkeratotic papules of the facial skin, especially on the eyelids, with episcleritis, proptosis, and papillomatous lesions on the tip of the tongue and lip mucosa. In addition, two nodules in the thyroid gland were detected. On laboratory examination, the carcinoembryonic antigen (CEA) was 34 ng/mL (normal limits: 0-3 ng/mL). Total thyroidectomy was performed. Histopathologic examination of the specimen revealed thyroid medullary carcinoma. After operation, levels of CEA decreased to normal limits.