Solitary intraductal papillomas (SIP) of the breast are relatively common lesions (incidence: 2-3%) originating from proximal ducts or from retroareolar lactiferous ducts. This work was aimed at evaluating the diagnostic reliability of US in the diagnosis of this condition and at discussing the differential diagnosis with similar focal lesions. Twelve cases of SIP were diagnosed with US among 31 selected female patients (aged 16-35 years) who had been referred for serohematic discharging breast and/or palpable nodules. All cases had surgical confirmation. US patterns typical of SIP were: 1) solid hypoechoic nodules with peripheral anechoic areas (7 cases); 2) small papillary excrescences within a cystic cavity, corresponding to papillary cystadenocarcinoma (4 cases); 3) periareolar overdistended ducts filled with dense material (1 case). Surgery was performed directly in 8 patients with positive cytology while mammography, ductography and fine-needle biopsy were performed in the extant 4 patients with negative or questionable cytologic findings. US combined with cytologic samples allowed the correct diagnosis to be made in 8 of 12 cases (66%): this is noteworthy when considering the low reliability of mammography in young patients and the poor tolerance to ductography in general. US allows the differential diagnosis with other focal lesions and subsequently helps shorten the diagnostic route.