Objectives. We examined the trends and correlates of quadrivalent human papillomavirus vaccine (HPV4) initiation in insured boys during the periods before and after routine use recommendation. Methods. We grouped data from electronic medical records of boys aged 9 to 17 years from the Kaiser Permanente Southern California prepaid health plan into 3 open cohorts: permissive use: 2009 to 2010; anal cancer indication added: 2010 to 2011; and routine use: 2011 to 2013. We estimated adjusted risk ratios (ARRs) between demographics and vaccination initiation using Poisson regression. Results. HPV4 initiation increased across cohorts—1.6%, 3.4%, and 18.5%—with the greatest increase among boys aged 11 to 12 years in cohort 3. Initiation was associated with receiving influenza vaccination in the previous year in all cohorts (cohort 3: ARR = 1.48; 95% confidence interval [CI] = 1.46, 1.51) and with non-White race/ethnicity following routine recommendation (cohort 3, non-Hispanic Black: ARR = 1.18; 95% CI = 1.08, 1.30; Hispanic: ARR = 1.23; 95% CI = 1.17, 1.29; Asian/Pacific Islanders: ARR = 1.16; 95% CI = 1.11, 1.20). Conclusions. Routine use recommendation increased the uptake of HPV4 in boys. System-level interventions to encourage providers to routinely recommend HPV4 vaccination may help increase HPV4 uptake in boys.