A 54-year-old HIV-positive homosexual man presented with erythematous and pigmented plaques on background erythema in the perianal region, histologically consistent with Bowen's disease. Perianal Bowen's disease represents high-grade anal intraepithelial neoplasia, which is considered a precursor lesion of invasive anal squamous cell carcinoma. This patient's anal intraepithelial neoplasia was unresponsive to multiple treatment modalities including cryotherapy, serial curettage and cautery, topical 5-fluorouracil and 5-aminolaevulinic acid photodynamic therapy. He progressed to develop a poorly differentiated squamous cell carcinoma of the anus three and a half years after the Bowen's disease was diagnosed. The squamous cell carcinoma was treated with combined chemoradiation. A recurrence of high-grade anal intraepithelial neoplasia was noted 6 months after completion of chemoradiation.