Using data from a large measles outbreak that occurred in Dane County (Wisconsin) in 1986, we conducted a case-control study to evaluate risk factors for vaccine failure and assessed the cost-effectiveness of school-based revaccination strategies. Vaccination before a change in the measles vaccine stabilizer in 1979 (odds ratio, 5.5; 95% confidence interval, 1.05 to 28.9) and vaccination before age 15 months (odds ratio, 13.9; 95% confidence interval, 5.9 to 32.6) were identified as risk factors. Revaccination strategies for all students ($3444 per case prevented), students vaccinated before 1980 ($3166 per case prevented), and students vaccinated before age 15 months($2546 per case prevented) were evaluated, assuming use of measles-mumps-rubella vaccine after the initial case was detected in a school. However, a large proportion of cases (43% to 53%) may not have been preventable using these strategies. Therefore, revaccination in all schools assessed to be at risk for measles may be necessary to prevent large outbreaks until a two-dose vaccination schedule is fully implemented.