The purpose of this study was to evaluate short- and long-axis diameters of enlarged cervical lymph nodes with ultrasonography and to determine whether the long-to-short axis (l/s) ratio is a valid diagnostic parameter in the differentiation between benign and malignant nodal disease. 730 enlarged cervical lymph nodes in 285 patients were examined with ultrasound. The short- and the long-axis diameters of each enlarged node were measured and the l/s ratio calculated. Definite diagnoses of the nodes were obtained by histological examination following neck dissection. 95% of enlarged cervical nodes shown on ultrasound to have a l/s ratio of more than 2 were correctly diagnosed as benign. Nodes presenting with a more circular shape and a l/s ratio of less than 2 were diagnosed correctly as metastases with 95% accuracy. The l/s ratio of lymph nodes thus provides an excellent criterion for differentiation between benign and malignant enlargement in cervical lymphadenopathy.