harmacists play an important role in protecting the public from the dangers posed by potential drug-drug interactions (DDIs), which have been identified as an important subset of medication errors.1 They are uniquely trained to recognize medication-related problems and have the opportunity to review the medication profiles of patients in the inpatient and outpatient setting before dispensing occurs.One of the tools that pharmacists rely on to review medication profiles for DDIs is computerized screening for DDIs. Computerized screening for DDIs and other potential drug-related problems is embedded within most pharmacy computer systems that are used in community and hospital pharmacies and also is included in the prospective, online drug utilization review provided by pharmacy benefit managers. While manual review of medication regimens can be performed by pharmacists, recognition of DDIs without the use of an aid (e.g., drug interaction reference, computer program) only identifies approximately 70% of DDIs in a 2-drug regimen and the proportion decreases substantially as the number of medications increases.2 Thus, computerized DDI screening has the potential to significantly improve the recognition of potentially harmful DDIs beyond what can be achieved with manual review alone. 3Research on the performance of computerized DDI screening software and the references they are based on have found problems in the ability to provide consistent information and screen for clinically significant DDIs. [4][5][6][7][8] For example, in 2001, Hazlet et al. ABSTRACTBACKGROUND: Computerized drug-drug interaction (DDI) screening is widely used to identify potentially harmful drug combinations in the inpatient and outpatient setting.OBJECTIVE: To evaluate the performance of drug-drug interaction (DDI) screening software in identifying select clinically significant DDIs in pharmacy computer systems in community and hospital pharmacies.