BACKGROUND Classic teaching has advocated the use of open biopsy to diagnose and grade extremity soft-tissue sarcoma. Reported advantages of core needle biopsy include the minimal morbidity, cost, and time. The perceived disadvantage has been diagnostic inaccuracy. The objective of this study was to compare the diagnostic accuracy of core needle biopsy to incisional or frozen section biopsy for primary extremity masses suspicious for soft-tissue sarcoma. METHODS Patients presenting with extremity masses were identified from our prospective soft-tissue sarcoma database (malignant) and from the clinical information center (benign) between January 1, 1990, and December 31, 1995. Biopsy and subsequent resection data were collected from the pathologic records. RESULTS During this time, 164 primary extremity soft-tissue masses were evaluated before any biopsy. As the initial diagnostic approach, there were 60 core needle, 44 incisional, 36 frozen section, and 26 excisional biopsies. Two patients underwent two biopsy procedures. Ninety-three percent of the specimens obtained at core needle biopsy were adequate to make a diagnosis. Of the adequate core needle biopsy specimens, 95%, 88% and 75% correlated with the final resection diagnosis for malignancy, grade, and histologic subtype, respectively. Of the frozen section biopsy specimens, 94% were adequate, and accurate diagnostic results of malignancy were obtained with 88%. However, only 62% and 47% were correct for grade and histologic subtype, respectively, which was significantly different than the results obtained with incisional biopsy. The false-negative and false-positive rates for core needle biopsy were 5% and 0% for malignancy. Two core needle biopsy specimens graded low were found to be high, and one core needle biopsy specimen graded high was subsequently found to be low on final resection. CONCLUSIONS When read by an experienced pathologist, the results of core needle biopsy provide accurate diagnostic information for malignancy and grade. Adequate core needle biopsy obviates the need for open biopsy and can be used for rational treatment planning. In the absence of adequate tissue, open biopsy is required.