One of the most important applications of breast ultrasound is to guide interventional procedures. During this presentation, we will discuss applications, indications, patient preparation, equipment selection, advantages and disadvantages and suggestions that will lead to the most successful results in the use of this procedure using this freehand technique. The main objective of this lecture is to analyse the use in a diagnostic, therapeutic and presurgical stage of the following procedures: fine-needle aspiration; large core biopsy; directional vacuum-assisted biopsy; presurgical localization in nonpalpable lesions. There are two principal approaches for freehand sonographically-guided procedures. One way would be to introduce the needle from the short end of the transducer which will give a clear view of both the needle tip and shaft. The other way would be to introduce the needle from the long axis of the transducer face, having the lesion visualized at its midpoint, with the disadvantage that only the needle point and not the shaft will be seen on screen. There are three fundamental aspects to bear in mind in interventionism: the guidance of the needle into the lesion, the procedure of obtaining the material itself and the cytopathologist’s experience. The main indications for obtaining material in solid lesions with the assistance of Ultrasound are: in tumours suspicious of malignancy, in order to confirm the diagnosis and investigate hormonal receptors and plan the most adequate therapy to apply; in images which do not concur with either the clinical evaluation or mammography results and are suspicious of malignancy; When there is more than one mass where the possibility for multifocal or multicentric malignant disease exists, in order to plan the treatment to follow; in any solid mass of any type, detected in the course of pregnancy or lactation. According to my experience, fine-needle aspiration proves successful with a sensibility of 91%, a specificity of 99.6% and a PPV of 95.8%, being 35% of the total of the lesions evaluated palpable and 65% of them nonpalpable. Core biopsies are made with activated guns using a 14-gauge needle, five passes being necessary in order to obtain enough material from the different areas of the lesion. The advantage of core-biopsy is the possibility to obtain more representative material for the histological evaluation making its accuracy to the final results a 100%. The directional vacuum-assisted biopsy is used in solid lesions bigger than 10 mm, taking only one penetration of the device to obtain several samples of material more representative in volume. For presurgical localization, we use carbon particles or hook-wire as markers, this procedure being successful in 100% of the cases. Conclusion: the importance of all the methods explained above is their role in lesions that are either nonconclusive, those which show doubtful images, in an early diagnosis and in order to avoid unnecessary surgical procedures. The sonographer plays a most important role in the diagnosis of nonpalpable lesions.