The association between thyrotoxicosis and thyroid cancer is a classical, rare and controversial entity. Within their series of eleven such cases the authors dissociate two distinct groups from clinical and pathological viewpoint. The first category is represented by one case of follicular thyroid cancer with clinically and biologically confirmed hyperthyroidism. The second group includes ten patients with thyrotoxicosis (three cases with Graves' disease, four with toxic multinodular goiter and three with toxic adenoma) and associated unsuspected occult or nodular carcinoma. None of these patients had received previous treatment with radioiodine. In all cases the diagnosis was established by pathological examination of the surgical specimen. Surgery is the treatment of choice in these lesions, the presence of carcinoma imposing the extent of operation. Five near total thyroidectomies and three near total lobectomies with ablation of the isthmus was performed in our cases associated with appropriate additional measures: TSH suppression or 131I treatment. Post surgical results were satisfactory without morbidity or mortality. The long-term survey was good (seven cases alive after 5 years).