Diffuse thyroid enlargement in a child is a rare presenting symptom of thyroid carcinoma. A papillary carcinoma may be hidden in a diffuse lymphocytic thyroiditis and should be carefully searched for during surgery. Furthermore, the finding, in frozen sections, of psammoma bodies in a lymphocytic thyroiditis should raise the suspicion of an occult malignant neoplasm. A case illustrating these diagnostic difficulties in a 5-year-old child is presented.