Yoon MA, et al. - A retrospective analysis of biopsy specimens collected from persons with soft-tissue tumors of the extremities and superficial trunk who underwent both ultrasound (US)–guided core needle biopsy (CNB) was carried out in order to assess the diagnostic outcome of US-guided CNB of soft-tissue tumors and to evaluate the factors related to notable diagnostic failure. For 40 of 303 biopsies, important diagnostic failure was recognized. Multivariate analysis revealed a notable relationship between diagnostic failure and adipocytic tumors or vascular tumors; intermediate (seldom metastasizing) biologic potential, or malignant biologic potential; and discordance between radiologic and final histologic findings or indeterminacy of biologic potential. In conclusion, independent risk factors for notable diagnostic failure of CNB of soft-tissue tumors are the World Health Organization classification categories (adipocytic or vascular), biologic potential (intermediate [rarely metastasizing] or malignant), and discordance between radiologic and final histologic findings or indeterminacy of biologic potential.