BACKGROUND Thyroid gland carcinomas usually appear as afunctional and hypofunctional lesions on thyroid scintigrams, but some rare cases of thyroid carcinoma with scintigraphic hyperfunctional lesions have also been reported. The aim of our retrospective study was to elucidate the frequency of carcinomas in patients operated for solitary hyperfunctional thyroid nodules and to represent their demographic and clinical features. METHODS During one decade (1997/2006), 308 patients were operated for solitary hyperfunctional thyroid nodules in the Centre for Endocrine Surgery in Belgrade. RESULTS Malignancy was revealed in 9 cases (about 3 %) by histopathological examination. In 6 cases papillary microcarcinomas were found adjacent to dominant hyperfunctional adenomas, while in 3 cases (about 1 %) real hyperfunctional carcinomas were confirmed. Follicular carcinoma was diagnosed in 2 cases and papillary carcinoma in one. All 3 patients were preoperatively hyperthyroid. In both patients with follicular carcinoma we performed lobectomies. In the third case we carried out a total thyroidectomy considering the intraoperative frozen section finding of a papillary carcinoma. CONCLUSIONS According to our results the frequency of solitary hyperfunctioning thyroid carcinomas is about 1 %, so that the possibility that a hyperfunctional nodule is malignant should be considered in the treatment of such lesions.