A 64-year-old Japanese woman was diagnosed as having Bowen's disease on the vulva. The histopathological findings revealed papillomatosis, koilocytosis and clumping cells with atypical nuclei. Human papillomavirus DNA was not detected on polymerase chain reaction using consensus primers. The lesion was successfully treated with topical imiquimod 5% cream after two months. Histopathologically, no atypical cells were observed after treatment. Imiquimod can be a potential treatment modality for lesions that are difficult to treat with surgical excision.