Purpose: To retrospectively analyze the positive predictive values (PPVs) of the lesions classified as categories 4 and 5 by using Breast Imaging Reporting and Data System (BI-RADS) ultrasonography (US). Materials and Methods: Between January 2012 and April 2012, the 558 lesion of 494 patients were reported BI-RADS US category 4 and 5. We reviewed the frequency, pathologic or clinical course. The PPVs for category 4a, 4b, 4c and 5 were evaluated. Results: Among the 558 lesions, the 395 lesions were pathologically confirmed as benign lesions and the 148 lesions were pathologically confirmed as malignant lesions. The 15 lesions were not pathologically confirmed. Among them, the 11 lesions were failed to follow up and 4 lesions are reassessed as category 3 lesions at the time of biopsy, which was scheduled to follow up rather than biopsy. The PPV for category 4 was 15.1% and the PPVs for subcategory 4a, 4b and 4c 5 were 7.8%, 60.0% and 78.1%. And the PPV for category 5 was 98.7%. Conclusion: In our hospital, the PPVs for BI-RADS US category 4a, 4b, 4c and 5 were presented to show the range of BI-RADS US, so it was appropriately subcategorized.