The study assessed the validity of the lymph node "roundness index" (RI) in the evaluation of enlarged lymph nodes of the neck. A total of 107 subjects were included in the prospective study, and 135 enlarged lymph nodes were examined. All the subjects were examined clinically and sonographically, the lymph node roundness index was determined, and soon after the nodes was surgically removed and pathohistologically diagnosed. On the basis of pathohistological diagnosis the study subjects were divided into two groups. The first group consisted of patients with benign lymph nodes, and the second one comprised patients with malignant nodes. The second group was further divided into two sub-groups: those with primary malignant nodes and those with secondary lymph nodes (metastases). The study showed that the lymph node RI statistically differs between the groups. In benign lymphadenopathy the RI was 1.66 ± 0.26, in primary malignant lymphadenopathy it was 1.31 ± 0.25 and in secondary malignant lymphadenopathy 1.13 ± 0.11. The analysis demonstrated that 82.9% of subjects randomly chosen from the group with primary malignant lymphadenopathy and 94.6% from the group with the secondary malignant lymphadenopathy have a smaller RI compared to randomly chosen subjects from the group with benign lymphadenopathy. Sensitivity of the method for primary malignant lymphadenopathy was 66.7% and specificity was 92.9%. For secondary malignant lymphadenopathy the sensitivity was 95.5% and specificity 92.9%. Based on this result we can conclude that the lymph node RI is a valid, simple, cost-effective and non-aggressive method which may "increase the suspicion" for a benign or malignant lymphadenopathy. RI ≤ 1.5 is indicative of malignant lymphadenopathy and RI ≥ 1.5 of benign lymphadenopathy.