Data from large clinical trials have shown that HPV vaccine can substantially reduce genital warts, cervical cytologic abnormalities and diagnostic and therapeutic cervical procedures when administered to pre-adolescent and adolescent girls. (1,2) Although modeling studies suggest that HPV immunization is cost-effective, (3-5) it remains a costly intervention. Given the expense of the vaccine series and its uniqueness, both in terms of a single gender approach and the availability of a secondary prevention strategy, it is essential that HPV immunization programs be evaluated in their local contexts. In August 2007, the province of Ontario announced plans to implement a publicly-funded, school-based HPV immunization program using Gardasil[R] vaccine beginning in the 2007-2008 school year. The Ontario program is locally administered by its 36 public health departments (Health Units [HUs]). Grade 8 girls (approximately 13 years of age) are eligible for publicly-funded vaccine using a 3-dose schedule administered over a 4 to 6 month period. The provincial program targets a single grade cohort and a catch-up component was not included. However, if a grade 8 girl receives at least one dose, she may complete the vaccine series in grade 9. This is referred to as "extended eligibility".