Background: Pharmacists and pharmacy technicians are essential to safe medication delivery. Filling prescriptions can be time consuming when the prescription is not complete or clear and requires inter-professional communication. To improve the quality and efficiency of dispensing medication we performed an audit of callbacks to physicians in the outpatient pharmacy associated with our cancer center with a focus on oral chemotherapy. Methods: The Princess Margaret is one of the largest cancer centers in the world, with an outpatient pharmacy on the premises that fills over 70,000 prescriptions a year. The pharmacists have access to the hospital’s Health Information System and chemotherapy prescribing system. A Prescription Audit Form was developed to track the mode of oral chemotherapy prescription (handwritten, preprinted, computerized physician order entry (CPOE), verbal) and reason for callback. The form was implemented from February 10th until March 7th, 2014 with coded data collection. The form was incorporated into the normal workflow of the outpatient pharmacy and concurrently used to document pharmacy interactions for billing purposes. Results: A total of 5,546 prescriptions were filled with 1,166 prescriptions for oral chemotherapy. Nine percent of prescriptions for oral chemotherapy required a callback to a physician and accounted for 32% of the total callbacks made to physicians. Of the 1,166 oral chemotherapy prescriptions; 39% were refills, 34% were handwritten, 22% were CPOE, 4% were verbal, 1% were preprinted, and 1% were not documented. The top two reasons for callbacks were; drug interaction (32%) and incorrect dose (24%). In the 9% of cases where the physician was contacted to clarify a prescription, the prescription was changed 43% of the time. Conclusions: Understanding the reasons for callbacks can be used to determine optimal data fields required in oral chemotherapy prescribing. Ensuring that prescriptions are appropriately completed will reduce the number of callbacks to physicians - significantly impacting the workflow and efficiency of the pharmacy. Reducing unnecessary callbacks will allow the pharmacy team to deliver timely, safe and effective patient centered care.