INTRODUCTION: In 2018, the Princess Máxima Center officially opened its doors as a national referral center for pediatric oncology in the Netherlands. This centralization of pediatric oncology also reshaped the pediatric neurosurgery landscape. Almost four years after centralization it is time to make up the balance. METHODS: From the start in May 2018, a predesigned database was kept for all neurosurgical procedures performed in the Princess Máxima Center, Utrecht. Data was collected by a

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... trained medical student and under close supervision of a pediatric neurosurgeon. Patient demographic data, tumor data (location, pathology), surgical data (approach, intended and obtained extent of resection), radiology data, and follow up data (complications, functional outcome) were collected. PRELIMINARY RESULTS: From May 2018 to December 2021, 783 oncology related surgeries have been performed in 472 individual patients (56% male; mean age 8 years). There were 316 cranial tumor resections, 279 of which were first resections. Pilocytic astrocytoma was the most frequent diagnosis (38%), followed by medulloblastoma (14%) and ependymoma (11%). Among the more rare tumors there were 29 diffuse midline gliomas and 29 craniopharyngiomas, reflecting the high volume after centralization. The extent of tumor resection and Clavien Dindo complication grading are correlated to time after centralization. CONCLUSION: Four years after the start of centralization, the pediatric oncology neurosurgery service in the Netherlands is well established. Clustering has resulted in high absolute numbers, even for rare tumor types, and growing experience. With this series we hope to create an international benchmark for pediatric oncology neurosurgery.