Despite decades of research on HPV vaccination, the U.S. has still not achieved optimal vaccination rates. This study investigated two different message strategies (agency assignment and deviance regulation marking) for encouraging HPV vaccination in two different populations: parents considering vaccinating their children and young adults (18-26) considering vaccinating themselves. Using a 2 × 3 × 3 online experiment, this study examined the differences between the two message target groups and the effects of the different message strategies on psychological precursors to HPV vaccination and vaccination intention. The findings indicate that using both agency and deviance regulation marking message strategies provided a significant increase in HPV vaccination intentions. However, there were many differences in terms of the variables influencing HPV vaccination decision making in young adults (18-26) and parents making decisions for their children. Specifically, using human agency and a deviance message increased HPV vaccine confidence in young adults, but did not in parents. Implications of these findings for designing different messages directed to these target groups along with future directions are discussed.