If properly performed, modern high-resolution real-time ultrasonography will disclose subtle differences in the texture of thyroid tissue and thereby enable the examiner to suggest a diagnosis. Nevertheless, there is often a need for a more specific diagnosis of solid or semisolid thyroid lesions - especially when the lesion might be malignant. Ultrasonically guided fine-needle aspiration biopsy (UG-FNB) allows a final cytological and/or histological diagnosis to be made in patients with benign or malignant space-occupying growths even if they are small. In its simplest form, thyroid nodules (diameter greater than 1.5 cm) with a uniform sonographic texture are punctured blind after determination of the site and size of the lesion on the basis of ultrasonic imaging. When the lesion is small and deeply situated (diameter less than or equal to 1.5 cm), this method will not be sufficiently accurate and more precise needle guidance is mandatory. In ultrasonically guided fine-needle puncture, the idea is to place the tip of an appropriate needle safely and accurately in the suspect lesion, so that representative specimens of solid tissue or fluid can be obtained and technical failures reduced. The main indication for biopsy of the thyroid gland is to differentiate between benign and malignant tumors. To compare the accuracy of conventional puncture techniques and ultrasonically guided puncture methods, 835 patients with benign or malignant space-occupying growth (even the small ones) were examined simultaneously with conventional and ultrasonically guided fine-needle aspiration biopsy over a period of 3 years (prospectively). Our results showed a significant difference in the sensitivity between conventional puncture without sonographic guidance and ultrasonically guided puncture techniques performed on patients with small and very small lesions (phi less than 2 cm). The size, macroscopic structure, and topographic-anatomical localization of the lesions were found to influence the diagnostic accuracy of the puncture techniques. UG-FNB is an excellent, effective, safe and painless method of treating uncomplicated thyroid cysts; it should be considered an alternative to surgery, if there are no clinical and cytological findings indicating malignancy and no severe space-occupying complications. Since the tip of the needle can be visualized on the scan, the needle may be advanced or withdrawn during aspiration so it is possible to empty the cyst completely. The use of ultrasound in the follow-up of patients with thyroid cyst puncture is mandatory to evaluate the results. Surgical therapy should be reserved for large cysts causing space-occupying complications.