Non-palpable breast lesions set histological problems. The authors with a series of 72 ultrasound guided cytology aspirations, describe the technique, its limits, its difficulties and its advantages. A biopsy was carried out on 51 lesions. The results were evaluated as follows: sensibility 86%, specificity 100%, positive predictive value 100%, false predictive value 97.5%. The diagnostic value of the method has been compared with other diagnostic tests (mammography, ultrasound and cytological puncture in palpable lesions). The procedure to be adopted has been suggested.