['The aim of this study was to evaluate heat shock protein 90 (HSP90) expression in squamous lesions (SLs) and to assess its diagnostic value for different lesions within the SL spectrum.', 'A total of 70 conjunctival SLs, including 19 papillomas, 22 cases of conjunctival intraepithelial neoplasia (ConINs) I, 11 cases of ConIN II, six cases of ConIN III, and 12 squamous carcinomas (sqCAs), were evaluated using the German immunoreactive score against HSP90.', 'Cytoplasmic HSP90 expression differed between low- and high-grade lesions (P < .001). Among high-grade lesions, the nuclear HSP90 score was higher in the ConIN III-sqCA group than in the ConIN II group (P = .0162). A percentage of total thickness staining of less than 73% differentiated between ConIN III and sqCA.'] Does analysis of HSP90 Expression be Valuable in the Differential Diagnosis of Ocular Surface Squamous Lesions?