BACKGROUND: Thyroid nodules are usually benign; however, 5 to 15% prove to be malignant. Fine-needle aspiration (FNA) has become the gold standard in the evaluation of thyroid nodules, especially in single nodule more than a centimeter and / or in smaller nodule with ultrasound characters of malignancy. METHODS: We evaluated retrospectively 179 patients with “undetermined” thyroid fine needle aspiration, undergoing surgery. We compared cytology and histology and we evaluated sex, age, the presence of thyroiditis and dimension of the indeterminate nodule as predictors of malignancy. RESULTS: In 48 patients (26.8%) histological examination confirmed the indeterminate cytological diagnosis and this means that the nodule underwent FNA was diagnosed in effects such as cancer. In 29 patients, on histological examination, the nodule underwent FNA was not diagnosed as cancer, but one or more carcinomas were diagnosed in the same lobe of indeterminate nodule, but in different location and / or in the contralateral lobe. In 102 patients, the definitive histological examination did not confirm the suspected diagnosis and we found a significant positive association only between male sex and histological malignancy. CONCLUSIONS: The indeterminate FNA still remains a challenge for the surgeon because it is not yet possible to discriminate patients who really need surgery from those that can be followed in follow-up. The potential of molecular diagnostics for thyroid nodules with indeterminate cytology is promising, but many of these markers are too complex or expensive for routine clinical use or are still poorly standardized.