The purpose of this article is to determine whether formal instruction regarding the BI-RADS ultrasound lexicon results in improved appropriate use of the lexicon. Ninety test questions depicting the features outlined by the 2003 BI-RADS lexicon were identified in our PACS. Informed consent was obtained from 34 radiology residents. The participants took the preinstruction test and then had 1 hour of formal instruction regarding the BI-RADS ultrasound lexicon, which included images depicting the different sonographic features and final assessment (including subcategories 4a, 4b, and 4c). The participants then completed the postinstruction test, which examined the same content. Test scores were calculated for both the pre- and postinstruction tests and then were compared by a linear mixed model and Wilcoxon signed rank tests. The participants' postinstruction test scores showed significant improvement in the overall use of the BI-RADS ultrasound lexicon (p < 0.0001). There was also significant improvement in the following specific areas: final assessment (p = 0.0005), margin (p = 0.0003), orientation (p = 0.0104), and lesion boundary (p = 0.0050). The categories for which test scores did not show significant improvement were echo pattern (p = 0.07), posterior acoustic features (p = 0.50), shape (p = 0.98), and subset of the final assessment (p = 0.24). Formal instruction regarding the BI-RADS ultrasound lexicon results in improved lesion characterization and final assessment.