OBJECTIVE: To evaluate a stepped-dose protocol for intralesional injection of cidofovir in children with recurrent respiratory papillomatosis (RRP). DESIGN: Prospective, nonrandomized case series. SETTING: Tertiary care children's hospital. PARTICIPANTS: Eleven children undergoing evaluation for RRP from June 1, 2000, through December 31, 2001. INTERVENTION: Intralesional injection of cidofovir was performed after microlaryngoscopy and carbon dioxide laser treatment. Patients received 4 monthly injections at a concentration of 5 mg/mL and returned 1 month after the last injection for follow-up. Patients with recurrent or recalcitrant disease then started a series of 4 monthly injections at a concentration of 10 mg/mL. OUTCOME MEASURE: Papilloma stage (0-3) documented at multiple subsites by means of serial microlaryngoscopy. We calculated a severity score by summing the scores at all affected subsites. RESULTS: The severity score decreased in each of the 11 patients during the course of therapy, from a mean +/- SD of 13.7 +/- 6.0 at enrollment to 2.1 +/- 3.4 at 1-month follow-up. Six patients experienced complete resolution (stage 0) and 4 others had mild disease (stage,