Objective To determine the relation between enlarged perihepatic lymph node (PLN) and viraemia,and to find out whether there is a difference in PLN size between the healthy individuals and patients with hepatitis C virus (HCV) infection. Methods Seventy-four patients with HCV infection and 283 healthy individuals were examined by two-dimensional ultrasound. The length and thickness of lymph node were measured. The lymph-node area index(LN area index) was calculated. The LN area index was evaluated by the ROC curve and compared with serum HCV core antigen (HCV-Ag) levels by correlation analysis. Results Detection rate, the length and thickness, LN area index of group with HCV infection were significantly different by compared with the normal control group ( P < 0. 001 ). The ROC curve showed that the LN area index as a diagnostic indicator had high sensitivity and specificity. The LN area index showed a significant correlation with HCV-Ag level (r = 0.436, P <0.05), but no significant differences were found between LN area index and HCV-Ag grade. Conclusions Perihepatic lymphadenopathy indicates viraemia,and LN area index of 100 mm2 is a reference index in estimating whether patients have HCV infection.