Parent hesitancy contributes to reduced HPV vaccination rates. The HPVcancerfree app (HPVCF) was designed to assist parents in making evidence-based decisions regarding HPV vaccination. This study examined if parents of vaccine-eligible youth (11-12 yrs.) who use HPVCF in addition to usual care demonstrate significantly more positive intentions and attitudes toward HPV vaccination and greater HPV vaccination rates compared to those not using HPVCF. Clinics (n = 51) within a large urban pediatric network were randomly assigned to treatment (HPVCF + usual care) or comparison (usual care only) conditions in a RCT conducted between September 2017 and February 2019. Parents completed baseline and 5-month follow-up surveys. Participant-level analysis determined 1) change in HPV vaccination initiation behavior and related psychosocial determinants and 2) predictors of HPV vaccine initiation. Parents (n = 375) who completed baseline and 5-month follow-up surveys were female (95.2%), 40.8 (±5.8) yrs. married (83.7%), employed (68.3%), college educated (61.9%), and privately insured (76.5%). Between-group analysis of HPVCF efficacy demonstrated that parents assigned to receive HPVCF significantly increased knowledge about HPV and HPV vaccination (