Background: Recently, American College of Radiology issued the latest 5th edition of BI-RADS Atlas which changed nomenclature and method to categorized breast composition.
Objective: To compare breast composition distribution between the 4th and the 5th edition of BI-RADS and to evaluate reader variability of breast composition according to the 5th edition.
Material and Method: Comparison of breast composition distribution between the 4th and the 5th edition of BI-RADS; interobserver and intraobserver agreement of breast composition of the 5th edition of BI-RADS between groups of readers were analyzed using 300 cases with mammography from January 2013 to December 2013.
Results: The breast composition distribution between the 4th and the 5th edition of BI-RADS had high correlation. The 5th edition BI-RADS had moderate to substantial interobserver agreement and substantial to almost perfect intraobserver agreement.
Conclusion: The breast composition distribution had no significant difference between the 4th edition and the 5th edition of BI-RADS. The 5th edition of BI-RADS also had good interobserver agreement among radiologists.

Keywords: BI-RADS, Breast density, Interobserver, Intraobserver