Cidofovir, a nucleoside analog antiviral agent, has been used with moderate success in the treatment of juvenile laryngeal papillomatosis (JLP) by direct intralesional injection. We report the first case where IV cidofovir was used successfully to treat a rare but lethal multicystic lung disease complicating JLP. A 35-year-old woman with a history of JLP requiring multiple laser ablations of laryngeal papillomata each year presented with hemoptysis and was found on CT scan to have bilateral, multiple pulmonary nodules and cysts. The results of BAL fluid analysis demonstrated no evidence of malignancy, and cultures were negative for fungi and mycobacteria. Molecular DNA typing of a biopsy specimen obtained from a laryngeal papilloma confirmed infection with human papilloma virus type 11. She received 12 months of treatment with IV cidofovir followed by 9 months of combined treatmentwith IV cidofovir and subcutaneous interferon-alpha-2A. This therapeutic regime resulted in a markedly decreased requirement for surgical removal of laryngeal papillomata, and CT scanning documented the regression of the lesions in the lung parenchyma that persisted after the discontinuation of therapy. The results of this case demonstrate that cidofovir may be used successfully to treat JLP-related lung disease and suggest that further studies are warranted.