Objectives: We sought to determine the diagnostic accuracy of ultrasound for benign and malignant breast lesions. Methods: This retrospective study was performed to evaluate the diagnostic accuracy of ultrasound in 203 patients with complete medical records who visited Mehr Medical Imaging Center for breast ultrasound between March 2014 and February 2016. The collected data comprised of demographic characteristics, ultrasound results (consisting of the anatomic area of the lesion, the involved side, and the ultrasound characteristics of the lesion), mammogram results, and pathology reports (if surgery or biopsy was performed). Results: For the diagnosis of malignant and benign lesions, ultrasound had a sensitivity of 93.9% and specificity of 86.5%; its positive and negative predictive values were 86.9% and 93.8%, respectively. Lesion type was significantly associated with a family history of breast cancer and fertility status (p < 0.005), but there was no significant association between the involved side and tumor type (p > 0.050). Conclusions: Mammography is the best technique for screening and identifying patients with non-mass-like breast lesions and microcalcifications. Considering the false positive and false-negative results, ultrasound is not a perfect screening modality. Future studies are recommended to study the value of ultrasound in the detection of high-risk breast cancer patients.