Ten years after its introduction, equity in human papillomavirus (HPV) vaccine uptake remains unattained, not least for the groups at highest risk of cervical cancer. In Sweden, three different delivery modes of the vaccine have been in effect since May 2007. We used this as a natural experiment to investigate girls' HPV vaccine uptake in relation to parental country of birth and socioeconomic characteristics, by mode of delivery. Our nationwide study cohort comprised 689,676 girls born between 1990 and 2003. Data on HPV vaccination of the girls and parental birth/socioeconomic characteristics were retrieved from national registers. We examined the association between girls' vaccine uptake and parental characteristics, stratified by mode of delivery. The cumulative uptake of at least one dose of HPV vaccine was 37%, 48% and 79% for subsidised opportunistic, free-of-charge catch-up outside-school and free-of-charge school-based vaccination, respectively. In the subsidised vaccination, having parents born outside of Sweden, with low education and low family income was strongly associated with lower uptake [HR (95% confidence interval (CI)) = 0.49 (0.48-0.50), 0.32 (0.31-0.33), 0.53 (0.52-0.54), respectively]. The associations were partially reduced in catch-up outside-school, and strongly reduced in school-based vaccination delivery [HR (95% CI) =0.82 (0.81-0.83), 0.92 (0.91-0.94), 0.87 (0.85-0.88), respectively]. Free-of-charge school-based HPV vaccination achieved the highest uptake and displayed the least disparity in country of birth and socioeconomic background of the parents. This appears to be the most effective and equitable delivery mode for reaching high population vaccination coverage, including high-risk groups for cervical cancer.