Objective: To assess the usefulness of cidofovir in treating recurrent respiratory papillomatosis in children. Cidofovir is an acyclic nucleoside phosphonate that has been reported to be effective in the treatment of respiratory papillomatosis in several small series of patients. Methods: A prospective study was conducted in 11 children (mean, 2.1 years; range, 0.5-3 years at diagnosis) with recurrent respiratory papillomatosis who at the start of the study were requiring debridement of papillomas at least every 6 weeks. After microlaryngoscopy with powered microdebridement of papillomas patients received intralesional injection of cidofovir (5mg/ml). The severity of papillomatosis was rated at each visit using a standardized papilloma severity scoring system. The success of therapy was measured by the trend in the patient's papilloma severity scores before and after cidofovir therapy and by whether the frequency of operative interventions decreased in the period after treatment began. Results: Three patients had impressive improvements in severity scores and a decrease in the frequency of required operative interventions after cidofovir, two patients had a partial response, and for six patients cidofovir was considered ineffective. Conclusions: Intralesional cidofovir did not decrease the severity or frequency of operative intervention for recurrent respiratory papillomas in the majority of children in this study. The drug did improve papillomatosis in the minority of patients without causing notable morbidity. A large multi-institutional controlled study is needed to better assess the efficacy of this treatment. © 2003 Elsevier Ireland Ltd. All rights reserved.