The purpose of this study was to evaluate the expression of claudins 1, 3M (membrane-bound), 3S (cytoplasmic), 4, 5 and 7 in vulvar epithelial neoplasia (VIN I-III) and to compare those with invasive vulvar squamous cell carcinoma. Paraffin tissue sections from 73 vulvar neoplasms (12 VIN I, 12 VIN II-III and 49 vulvar carcinomas) were studied by immunohistochemistry for the expression of claudins 1, 3M, 3S, 4, 5 and 7. Claudin 1 stained strongly in all groups, whereas claudin 3M, 3S and 4 immunostaining were moderate in all groups. Claudin 7 stained strongly in all groups. Claudin 3M expression was higher in VIN I compared to carcinoma, while no difference was found between VIN I and VIN II-III or between VIN II-III and carcinoma. Claudin 1 and claudin 3S expressions also showed the same decreasing tendency from VIN towards vulvar carcinoma. Claudin 5 showed only weak staining in VIN I and VIN II-III, and positive expression was also low in the carcinoma group. Expressions of claudins 1, 3M, 3S, 4 and 7 were found in VIN and vulvar carcinoma. Changes in claudin 1 and claudin 3 expression during progression from VIN to vulvar carcinoma suggests a connection with claudin expression and differentiation of vulvar squamous cells. Claudin 5 does not seem to be important in VIN or vulvar carcinoma.