To determine if use of the five final assessment categories of the American College of Radiology's Breast Imaging Reporting and Data System (BI-RADS) improved objectivity or accuracy of mammographic evaluation in 40- to 49-year-old women, fifty mammograms of 40- to 49-year-old women that were obtained at a tertiary referral teaching hospital were classified according to those five final assessment categories. The mammograms were blinded to six American Osteopathic Board of Radiology-certified radiologists who were asked to classify each mammogram within the five final BI-RADS categories based on the mediolateral oblique and craniocaudal views presented. No history was allowed. Use of the BI-RADS five final assessment categories provided moderate interobserver objectivity, moderately high agreement among the radiologists' interpretation (reliability), and moderate accuracy of interpretation (validity) when compared to criterion. Moderate interobserver reliability and accuracy has been previously identified; however, no scientific review of the BI-RADS five final assessment categories in 40- to 49-year-old females was discovered in the current literature. No overall improvement of objectivity or accuracy was demonstrated using the five final assessment categories of the BI-RADS lexicon in 40- to 49-year-old women.