Diagnosis is the critical first step in diagnosing soft tissue masses especially soft tissue sarcomas (STS) like rhabdomyosarcoma (RMS) in the pediatric population. Historically, incisional biopsy (IB) was the preferred route. The objective of this chapter was to evaluate core needle biopsy (CNB) compared to IB and fine needle aspirate (FNA) related to diagnostic accuracy, nondiagnostic samples, and complications. We performed a systematic review of the current literature relating to STS and RMS in adults and children. CNB had high diagnostic accuracy of malignancy (85–100%) and high diagnostic accuracy of histology subtype (sensitivity of 88% and specificity of 77%); both of which were equivalent to IB in a meta-analysis. The nondiagnostic rate of CNB ranged from 2% to 14%, nonetheless was not significantly different from IB. A meta-analysis found CNB to be associated with a significant reduction in the risk of complications over IB. CNB was also associated with reduced days to present at tumor board. Based on this systematic review, CNB can be effectively used for biopsy in the diagnosis of RMS in pediatric patients with less morbidity compared to IB.