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BACKGROUND Phyllodes tumors are fibroepithelial breast lesions that are uncommon in women and rare among children. Due to scarcity, few large pediatric phyllodes tumor series exist. Current guidelines do not differentiate treatment recommendations between children and adults. We examined national guideline adherence for children and adults. METHODS We queried the NCDB (2004-2014) for female patients with phyllodes tumor histology, excluding patients with missing age or survival data. Patients were stratified by age (pediatric <21, adult ≥21), and compared based on patient characteristics, treatment patterns, and survival. RESULTS We identified 2787 cases of phyllodes tumor (2725 adult, 62 pediatric). Median age was 17years in children and 52years in adults. Margin positivity rates and median tumor size were similar between adults and children. Treatment was discordant with NCCN guidelines in 28.6% of adults and 14.5% of children through use of axillary staging, chemotherapy, adjuvant endocrine therapy, and radiotherapy. Five-year and ten-year survival were comparable between both groups. CONCLUSION Children and adults present with similarly sized phyllodes tumors. Trends reveal high margin positivity rates, and overtreatment with regional axillary staging and systemic adjuvant therapies. Particularly in children, treatment decisions must consider risks of adjuvant therapy including radiation-related second primary cancers, given uncertain benefit. TYPE OF STUDY Retrospective Comparative Study. LEVEL OF EVIDENCE Level III.