Purpose: This study sought to determine the previously undescribed cytologic and metabolic alterations that accompany endoscopic third ventriculostomy with choroid plexus cauterization (ETV/CPC). Methods: Cerebrospinal fluid (CSF) samples were collected from infant patients with hydrocephalus at the time of index ETV/CPC and again at each reintervention for persistent hydrocephalus. Basic CSF parameters, including glucose, protein, and cell counts, were documented. A multivariable regression model, incorporating known predictors of ETV/CPC outcome, was constructed for each parameter to inform time-dependent normative values. Results: A total of 187 infants were treated via ETV/CPC for hydrocephalus; initial laboratory values were available for 164 patients. Etiology of hydrocephalus included myelomeningocele (53, 32%), intraventricular hemorrhage of prematurity (43, 26%), aqueductal stenosis (24, 15%), and others (44, 27%). CSF parameters did not differ significantly with age or etiology. Glucose levels initially drop below population average (36 to 32 mg/dL) post-operatively before slowly rising to normal levels (42 mg/dL) by 3 months. Dramatically elevated protein levels post-ETV/CPC (baseline of 59 mg/dL up to roughly 200 mg/dL at 1 month) also normalized over 3 months. No significant changes were appreciated in WBC. RBC counts were very elevated following ETV/CPC and quickly declined over the subsequent month. Conclusion: CSF glucose and protein deviate significantly from normal ranges following ETV/CPC before normalizing over 3 months. High RBC values immediately post-ETV/CPC decline rapidly. Age at time of procedure and etiology have little influence on common clinical CSF laboratory parameters. Of note, the retrospective study design necessitates ETV/CPC failure, which could introduce bias in the results.