Vaccination prevents Human papillomavirus (HPV) associated diseases. This study is a cost-utility analysis about adding boys to the HPV immunization program for girls in an Albertan and Canadian context, using a decision tree based model. Individuals in Grade 5 can be a boy or girl, and vaccinated or not vaccinated. Then, they can get a disease; and either survive or die. Included diseases were cervical, anal, head and neck, vaginal, vulvar, penile cancers, and anogenital warts. Parameters were adjusted to 2016 Canadian dollar and discounted 5% annually. The incremental cost effectiveness ratio (ICER) per quality adjusted life years for adding boys to the girls-only vaccination is $333,420. In sensitivity analysis, discount rate and herd immunity had the largest impact. Given the female coverage rate in Alberta, additional vaccination of boys would not be cost-effective because herd immunity reduces benefits. Policy justification of adding boys should expand beyond cost-effectiveness.