The dense breast is the one composed primarily of fibroglanduhar tissue which appears darker at mammography. It is difficult to achieve good contrast throughout a mammogram in women with extensive mammographically dense tissue, which can obscure some of the subtle signs of breast abnormalities consequently; it is more difficult to diagnose breast cancer in such women. We evaluated the role of ultrasonography in detection, characterization and localization for percutaneous biopsy of breast lesions in patients with mammographically dense breast. Study included 60 female patients (age range from 20-80 years) complaining of mastalgia, breast swelling or nipple discharge with dense breast. Patients were subjected to 1. Full history, 2. Clinical examination, 3. Mammography, 4. Breast ultrasound, 5. Biopsy and histopathyologyin patients with a suspicious lesion, 6. Sonographic findings of the dense breast were categorized according to the BI-RADS. Mammographic findings were normal in 31 patients and abnormal in 29 patients (mass, LNs, asymmetric density, and calcification). Ultrasound was –ve in 4 patients and +ve in 56 patients. BI-RADS 2 and 3 were the commonest US findings. The diagnostic category of ultrasonography and mammography was statistically tested for their reliability for diagnosing and for differentiating between benign and malignant lesions using the pathological diagnosis as a gold standard. Ultrasonography had a diagnostic reliability for diagnosing and for differentiating between benign and malignant breast lesions (p=0.869) in mammographically dense breasts while mammography was diagnostically unreliable for detecting and diagnosing breast lesions (p=0.045).