OBJECTIVE. We evaluated the overall effect of Illinois’ school-entry mandate on hepatitis B vaccination coverage levels and racial/ethnic differences in vaccination coverage before and after the mandate. METHODS. In 1997, the Illinois Department of Public Health mandated hepatitis B vaccination before entry into 5th grade. We conducted a retrospective cohort study of 6 consecutive Chicago public schools’ 12th-grade classes; 4 entered 5th grade before the mandate (premandate cohorts) and 2 afterward (postmandate cohorts). We used Chicago public schools’ vaccination database and calculated annual coverage levels for 2nd through 12th grades; the cohorts entered 12th grade during 2000–2005. We compared hepatitis B vaccination coverage levels according to race/ethnicity and coverage levels for the premandate and postmandate cohorts. RESULTS. We evaluated 106 541 students. The postmandate cohort had significantly higher hepatitis B vaccination coverage levels than the premandate cohort at 5th-grade (38.2% vs 4.3%) and 9th-grade (85.0% vs 37.4%) entry. For 9th-grade students, compared with white students, black students were less likely to have received hepatitis B vaccination before the mandate; this disparity decreased for the first postmandate cohort. For Hispanic students, the disparity was less pronounced and also decreased after the mandate. By 9th grade in the postmandate cohorts, coverage levels for all racial/ethnic groups exceeded 80%. CONCLUSIONS. There was a dramatic decrease in the disparity of hepatitis B vaccination coverage between white and black or Hispanic students. School-entry requirements effectively increased hepatitis B vaccination coverage levels regardless of race or ethnicity and should be considered for other recently recommended adolescent vaccines.