Background: Medication prior authorization (PA) is a commonly occurring requirement, particularly for medications used for rare conditions. Based on standard definitions, cancer and many blood disorders affecting children are rare. The study aims were to describe the relative frequency of PA requests and their association with payers and medications in order to identify opportunities to improve system efficiency. Procedure: Requests for medication PA were logged prospectively for patients seen at a single institution over a 7-month period. Period prevalence was used to estimate the relative frequency of PA requests. Descriptive statistics summarized the relationship among payers, medications, and approvals relative to the frequency of PA requests. Results: For the study duration of 150 clinic days, there were 5,583 patient visits. A total of 142 medication PA requests were received resulting in a period prevalence rate of 2.5% patient visits. Of the 137 medication PA requests with available outcome data, 135 (98.5%) were ultimately approved with additional provider efforts. The median clinic staff time spent per request was 46 min with an interquartile range of 25-80 min. There was striking process heterogeneity among different payers. Conclusion: Virtually no medication PA request in pediatric hematology and oncology (PHO) leads to alterations in care. Medication utilization management strategies in PHO fail to provide benefits reported in other areas of medicine and have unmeasured negative effects on timeliness of care and parenteral psychological/emotional health. There is opportunity for increasing efficiency through payer and provider collaboration on the creation of prescribing standards for PHO patients.