Human papillomavirus is highly prevalent. Certain subtypes are oncogenic and many are responsible for a wide range of disease. HPV types 16 and 18 cause about 70% of cervical cancers. Most of the remaining cases of cervical cancer are caused by other types of HPV. HPV types 16 and 18 are also associated with vulvar, vaginal, penile, anal, and oropharyngeal cancers. HPV types 6 and 11 cause approximately 90% of genital warts. The prevalence of infection is high but varies widely across populations. One recent study conducted in the United States, Brazil, and Mexico examined men who have sex with women and men. In this population, with a mean age of 32.5 years, 53.1% were infected with HPV1 and 30% were infected with oncogenic strains. A larger sample of women in the United States documented an overall prevalence of 26.8%. The highest prevalence was in women aged 20 to 24 years, 44.8% of whom were infected.2 An estimated 22 000 cancers associated with HPV types 16 and 18 occur annually in the United States.