OBJECTIVES: Describe human papillomavirus (HPV) vaccine uptake, initiation, completion, compliance, and missed vaccination opportunities among patients before and after introduction of 9-valent HPV vaccine (HPV9). METHODS: A retrospective patient cohort, males & females aged 9 to 26 years, enrolled in the Kaiser Permanente Northwest health plan between April 2012 and June 2016 was selected (N = 244,491). Vaccination and health care utilization data from electronic medical records and state-wide immunization registry were analyzed. Vaccine uptake (number of doses administered) was assessed during 4-month periods. Vaccine initiation, completion, compliance (received 3 doses within a 9 month period), and missed opportunities (eligible patient visits with no vaccination) were assessed over the entire study period and over 1-year periods pre- and post-HPV9 introduction in July 2014. RESULTS:  Approximately 9,000 doses were administered during each 4-month period, with increases during periods spanning August through November (approximately 11,000 doses administered). During the study period, initiation was highest among patients aged 13 to 21 years, at 55%. Among those who initiated the series, 71.1% of patients completed two doses and 48.2% completed three doses of HPV vaccine; 28.2% were compliant with guidelines during the study period. Compliance was slightly lower prior to HPV9 introduction than during the post-period (21.3% and 28.0%, respectively). The proportion of patients with at least one missed vaccination opportunity was similar pre- and post-HPV9 introduction (56.0% and 53.6%, respectively). CONCLUSIONS: Uptake peaked at the start of the academic year. Among initiators, less than half completed three doses and few complied with dose-spacing recommended by the ACIP during the study period. Missed opportunities were common; reducing such occurrences may lead to higher completion and compliance as well as earlier immunization. Further analysis of reasons for missed opportunities and adolescent/young adult resource utilization may inform health care systems on improving HPV vaccine uptake and schedule compliance.