The aim of this study was to determine whether viral type (HPV-6 vs. HPV-11) could predict the clinical course of recurrent respiratory papillomatosis in children. Viral typing, using the polymerase chain reaction, was performed on laryngeal biopsies of 61 patients treated at Children's Hospital of Michigan. HPV-6 was detected in 29 of the patients' biopsies and HPV-11 in 32 biopsies. HPV-11 was more common among the African-American patients than among Caucasians (P = 0.001). Patients with HPV-11 were diagnosed at a younger age (36.2 vs. 48.2 months; P = 0.04) and were more likely to have active disease (P = 0.0311) at the time of this study. They tended to have longer periods of disease activity (8 years vs. 5 years; P = 0.026), required more surgical procedures (42 procedures/patient vs. 13.6; P = 0.02), and more procedures per patient, per year (2.9 vs. 5.3; P = 0.0164). Three of the patients infected with HPV-11 developed invasive papillomatosis and bronchogenic squamous cell carcinoma, and two of these patients died of disease. Our findings suggest that HPV-11 infection confers a more aggressive course to recurrent respiratory papillomatosis.