Ultrasound (US) and US-guided fine-needle aspiration biopsy (FNA) were performed in 91 nonpalpable neck nodes of 70 patients, 98% of which had known malignancy. Various sonographic findings were evaluated for predicting malignancy. The accuracy of US-guided FNA for detecting malignancy was 88%, with 96% sensitivity and 94% specificity. The ratio of minimal to maximal axial diameters of a node was most valid for predicting malignancy with US. A ratio of more than 0.55 yielded the highest accuracy (80%) (92% sensitivity, 63% specificity). Addition of any other factors to this criterion did not improve its accuracy. US and US-guided FNA are accurate for the assessment of nonpalpable neck nodes. Lymph nodes with a round configuration should be biopsied in patients with known malignancy.