This paper report a case of autonomously functioning thyroid nodule, firstly occurred in a 13 years old women, complicated 9 years later by hyperthyroidism, with no response to thyreostatic treatment, hystologically diagnosed as papillary carcinoma, in a thyroid gland affected by Hashimoto's thyroiditis, with cervical bilateral lymph node metastasis. In literature the rate of coexisting hyperthyroidism, chronic thyroiditis and differentiated carcinoma is low; thus thyroid malignancies are very rare in young people. In this patient the large autonomously functioning nodule was entirely made of neoplastic tissue, while in the remaining thyroid there was no evidence of adenomatous tissue. Moreover, thyreostatic treatment failed in controlling hyperthyroidism. The Authors consider these facts as indirect evidences that this is a rare case of hyperfunctioning differentiated thyroid carcinoma.