Objective. The primary purposes of this study were to: 1) determine the extent to which multitasking affects the speed and accuracy with which professional-phase pharmacy students identify prescription errors and 2) determine if there is a relationship between students' self-perception of their multitasking ability and their actual ability. Methods. 121 second-year pharmacy students enrolled in Introduction to Dosage Forms spent one week in the experimental (multitasking) condition and one week in the control (undistracted) condition. Subjects were given 10 minutes to check 10 prescriptions and record any identified filling errors. A cellular phone was placed in each room. Subjects in the experimental (multitasking) condition answered a call from a researcher posing as a chatty customer during the prescription-checking task; those in the control condition were not interrupted by a cell phone call during the task. Subjects' completion times and accuracy were recorded. Results. When subjects where multitasking, they took significantly longer to complete the prescription-checking task than when they were not multitasking. Furthermore, when subjects were multitasking, they scored significantly lower on the prescription-checking task than when they were not multitasking. Finally, students' self-perceptions of their multitasking abilities were not related to the speed with which they completed the prescription-checking task nor to their accuracy. Conclusion.Multitasking negatively affects speed and accuracy of prescription verification in student pharmacists. Our procedure can be used as an in-class activity to demonstrate attentional limitations and to shape how future pharmacists practice.