Increased cyclooxygenase-2 (COX-2) expression has been observed in both squamous cell carcinoma (SCC) and adenocarcinoma (AC) in Western countries, and COX-2 inhibitors have been considered as potential chemopreventive agents for esophageal cancers. Since chemoprevention often targets the premalignant lesions in high-risk population, it is worthwhile to study COX-2 expression in a spectrum of premalignant and malignant lesions obtained from the high-risk populations. In this study, biopsy samples were taken from 240 subjects identified by screening of the high-risk population in Cixian, China, including 27 normal, 29 with squamous hyperplasia, 84 with dysplasia (31 low grade and 53 high grade), 30 with carcinoma in situ, and 70 with invasive carcinoma (60 SCC and 10 AC). For comparison, tissue samples were also collected from He Lon Jiang Province, a low-risk population in China, including 10 patients with invasive SCC, 20 patients with AC, and 17 patients with Barrett's esophagus. The COX-2 protein expression was examined by immunohistochemistry. Using 10% staining as a threshold, 9 of 10 (90%) invasive SCC from low-risk population were COX-2 positive. However, no positive COX-2 staining was seen on normal, hyperplastic, dysplastic, and in situ squamous lesions from the high-risk population, and only 4 of 60 (6%) invasive SCC exhibited positive COX-2 staining. For glandular lesions, 6 of 10 (60%) AC from high-risk area and 15 of 20 (75%) from low-risk area showed positive COX-2 staining, and 12 of 17 (70%) premalignant Barrett's esophagus were also positive. Our findings show that COX-2 expression various in squamous lesions from high- and low-risk areas, but not in glandular lesions. Additional studies are needed to fully explore the mechanisms that are associated with the different COX-2 immunohistochemical staining patterns in esophageal squamous lesions from low- and high-risk populations.