Background. Uptake of human papillomavirus (HPV) vaccine among girls in the Dutch immunization program has plateaued at around 60%. Vaccinating boys may be an appealing complementary strategy for the prevention of HPV-related diseases, especially since tender negotiations and reduced dosing schemes have driven down the cost of vaccination. Methods. We expanded a previously published Bayesian synthesis framework to account for all vaccine type-related cancers and herd immunity effects from vaccinating girls and boys. We evaluated the efficiency of vaccinating boys relative to increasing vaccine uptake among girls and assessed the cost-effectiveness of a sex-neutral program. Results. Vaccinating 40% of boys along with 60% of girls yielded the same gain in life-years (LYs) as increasing the uptake in girls from 60% to 80%. The incremental cost-effectiveness ratio (ICER) of vaccinating boys was 9134/LY (95% credible interval [CrI], 7323/LY-11 231/LY) under 3% discounting. The ceiling vaccination costs at which the ICER remained below the per capita gross domestic product threshold was 240 (95% CrI, 200-280) per vaccinated boy. If girls' uptake increased to 90%, the ceiling costs decreased to 70 (95% CrI, 40-100) per vaccinated boy. Conclusions. Vaccinating boys along with girls is only modestly less efficient than increasing uptake among girls and highly likely to be cost-effective under current vaccine costs and uptake in the Netherlands.