Controversy still exists about the ability to differentiate between malignant and benign Hürthle cell tumors (HCTs) before and during surgery. Diagnostic difficulties make surgical decisions debatable. The aim of this study was to evaluate factors predicting the malignancy of HCT and to plan its appropriate management. From January 1998 to May 2003 a series of 41 patients underwent thyroidectomy in our surgical department because of HCT. A cross-sectional study of 23 patients with carcinoma and 18 patients with adenoma was carried out: demographic data, tumor characteristics, diagnostic results of fine-needle aspiration cytology (FNAC), frozen section (FS), MIBI scan scintigraphy, surgical indications, and treatment were evaluated. The mean tumor size was significantly greater for carcinomas than adenomas (3.1 vs. 1.9 cm; p = 0.006). Threshold sizes of more than 3.0 cm and 4.0 cm, respectively, were significant for predicting malignancy (p = 0.025 and p = 0.012). Conversely, 47.8% of carcinomas had a diameter smaller than 3.0 cm. FNAC and FS sensitivities for carcinoma detection were 23.8% and 33.3%, respectively. The positive uptake on MIBI scan imaging was likely to be similarly malignant or benign. Because of the lack of accuracy of all diagnostic studies for predicting malignancy, all oxyphilic cell nodules should be referred to surgery. Different tumor sizes cannot be the only factor on which to base a surgical decision. Therefore, because of diagnostic uncertainties, we believe that an experienced surgeon can safely perform total thyroidectomy in all patients with an HCT.