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PURPOSE The best method for diagnosing pediatric nonnephroblastoma solid intraabdominal tumors is unknown. We hypothesized that core needle biopsy (CNB) is noninferior to open wedge biopsy (OWB) for pathologic diagnosis. METHODS We prospectively enrolled children aged 1day to 17years with radiographic evidence of nonnephroblastoma solid intraabdominal tumors scheduled for OWB from 5/2013 to 12/2015 at a single institution. Four 16-gauge CNBs were obtained, followed by OWB. Two pathologists independently reviewed all specimens to determine adequacy for diagnosis. RESULTS Fourteen patients enrolled, 57% male, with an average age of 4years (range 7days to 16years). Both pathologists agreed OWB was completely sufficient for diagnosis in 13 patients (93%), compared to 4 patients for CNB (29%: Burkitt lymphoma, adrenocortical tumor, inflammatory myofibroblastic tumor, p=0.001, δ=-0.64±0.27, 95% CI). In 6 patients (43%), CNB was incompletely diagnostic according to at least one pathologist (neuroblastoma, hepatoblastoma). In 4 patients (29%), both pathologists determined that CNB was nondiagnostic (ganglioneuroblastoma, teratoma, hepatoblastoma, and recurrent neuroblastoma). CONCLUSIONS In a prospective clinical study, CNB is inferior to OWB for the pathologic diagnosis of pediatric nonnephroblastoma solid intraabdominal tumors. These data suggest that OWB should generally be performed in these patients. LEVEL OF EVIDENCE Study of Diagnostic Test, Level I.