['We hypothesized that ultrasound characteristics of breast fibroadenomas (FA) vary in relation to the clinical and histological parameters: patient age, tumor size and histological classification.', 'Eleven ultrasound characteristics frequently observed in breast tumors were defined before the onset of our study. These characteristics, as well as a semi-quantitative score for vascularization on color-coded Doppler ultrasound, were analyzed in a retrospective study. Histology revealed adult type differentiation in all FA. They were divided into florid, regressive and mixed subtypes. The examiner was blinded for the histological classification during image analysis.', 'Histological type: florid FA: more frequent in younger women (age group < 30 years; p < 0.001), and bigger than regressive FA (larger than 16 mm: p = 0.007). Statistically significant differences between florid and regressive FA regarding the ultrasound features: enhanced posterior ultrasound transmission (p < 0.001), homogenous echo pattern (p = 0.003) and lobulated margin contour (p = 0.042). Tumor size: patients with larger tumors (> 16 mm) were younger (mean age 35 vs. 43 years, p < 0.001). More often in bigger FA: enhanced dorsal ultrasound transmission (p < 0.001), hyperechoic spots (p < 0.001), strong vascularization (p < 0.001), inhomogeneous echo pattern (p = 0.001), horizontal axis (p = 0.009), lobulated margin contour (p = 0.009), lateral shadowing (p = 0.047). Age: more often in older patients (age group > 30 years): dorsal ultrasound shadowing (p = 0.008), irregular margin contour (p = 0.038), homogenous echo pattern (p = 0.047).'] Are ultrasound characteristics of breast fibroadenomas related to clinical and histological parameters?