BACKGROUND Nucleolar organizer regions (NORs), which are loops of DNA containing ribosomal RNA genes, have been shown to correlate with cell proliferation and malignant transformation. Conventional eyeball measurement of silver staining NORs (AgNORs) is time-consuming and subject to error. The diagnostic value of AgNOR area in nasopharyngeal carcinoma (NPC) by computer-assisted morphometric analysis is evaluated. METHODS Silver-staining of NORs was applied to 23 paraffin sections of NPC containing both normal squamous epithelial and malignant cells. Various parameters of the AgNORs of these two cell types were analyzed by a computer-assisted image analysis system and then compared. RESULTS The mean AgNOR area, AgNOR/nuclear area ratio, and AgNOR area/count ratio of malignant tumors were statistically significantly higher than those for the normal epithelium. There was no significant difference in the AgNOR counts between the two cell types. CONCLUSIONS Computer-assisted morphometric analysis of AgNOR is an objective and reliable assessment method applicable to paraffin sections of NPC. The AgNOR area and its derivatives may aid in the diagnosis of NPC.