Patients apply topical cidofovir to the perianus once daily on days 1-5. Patients undergo punch biopsy of pretreatment lesional biopsy sites on day 14. Beginning 2-4 weeks after biopsy, patients receive course 2 of cidofovir therapy. Subsequent treatment repeats every 14 days for up to 6 courses* in the absence of disease progression or unacceptable toxicity.