A descriptive correlational research design assessed factors influencing participation and completion rates, and to determine vaccine administration costs, in a school-based Hepatitis B vaccination program. Of 18,046 students in public and private schools in the metropolitan Kansas City, Mo., area, 12,986 (73.4%) participated with approximately 75% of these students completing the vaccine series. Larger schools reported decreased participation and completion rates. Both rates were highest in schools providing educational interventions. Schools with a large population of commercially insured students reported low participation rates (65%), but high completion rates (85%). Schools with a high number of Medicaid-eligible students had high participation rates (97%), but low completion rates (67%). The vaccine cost $5.06 per dose to administer.