Background: The most common childhood central nervous system cancer in the United States (US) is pediatric low-grade glioma (pLGG). However, pLGG is not readily identified in cancer registry data because there is no standardized set of International Classification of Diseases for Oncology, 3rd Edition (ICD-O-3) codes to define pLGG. Identification of these patients is essential to understanding this disease. Methods: The objectives of this retrospective study are to: 1) identify ICD-O-3 codes for a pLGG as a definition template, and 2) describe the pLGG incidence in the US using 2015-2019 data from the CBTRUS, an aggregation of data from the CDC’s National Program of Cancer Registries and NCI’S Surveillance, Epidemiology, and End Results program. These years were selected to obtain the latest data without the potential impacts of COVID-19. To define pLGG, ICD-O-3 codes were identified based on comprehensive literature reviews. Average annual pLGG incidence was calculated in US patients aged 0-18 years overall, by grade and by ICD-O-3 code. Grade was defined by Collaborative Staging Site-Specific Factor 1: WHO Grade (2015-2017 diagnoses) and by Grade – Pathological (2018-2019 diagnoses). Results: Eighteen ICD-O-3 codes defined pLGG in this study. Between 2015 and 2019, average annual new cases of pLGG for those aged 0-18 years was 1,934. Among all patients diagnosed in 2015-2019, 40.7% had an unknown tumor grade (N=787). The most frequent diagnosis was pilocytic astrocytoma, malignant (ICD O-3 code 9421/3). The annual average incidence for pilocytic astrocytoma was 731, which comprised 37.8% of pLGG in 2015-2019. Discussion and Conclusions: Identification of patient populations with pLGG is complex. Unknown tumor grade comprises a substantial proportion of patients; therefore, selection of those classified as low-grade underestimates pLGG incidence. This study provides a comprehensive definition of pLGG to fill the current research gaps and accurately describes pLGG incidence in the US.