Introduction: Vaccination against human papillomavirus (HPV) is routinely recommended for ages 11-12, yet in 2016 only 49.5% of women and 37.5% of men had completed the three-dose series in the United States. Offering information and cues to action through a serious videogame for preteens may foster HPV vaccination awareness, information seeking, and communication. Materials and Methods: An iterative process was used to develop an interactive videogame, Land of Secret Gardens. Three focus groups were conducted with 16 boys and girls, ages 11-12, for input on game design, acceptability, and functioning. Two parallel focus groups explored parents' (n = 9) perspectives on the game concept. Three researchers identified key themes. Results: Preteens wanted a game that is both entertaining and instructional. Some parents were skeptical that games could be motivational. A back-story about a secret garden was developed as a metaphor for a preteen's body and keeping it healthy. The goal is to plant a lush secret garden and protect the seedlings by treating them with a potion when they sprout to keep them healthy as they mature. Points to buy seeds and create the potion are earned by playing mini-games. Throughout play, players are exposed to messaging about HPV and the benefits of the vaccine. Both boys and girls liked the garden concept and getting facts about HPV. Parents were encouraged to discuss the game with their preteens. Conclusion: Within a larger communication strategy, serious games could be useful for engaging preteens in health decision making about HPV vaccination.