Serological screening of 5470 children age 7.5 years from a cohort of 13,971 children in the Avon Longitudinal Study of Parents and Children (ALSPAC) suggested the prevalence of celiac disease (CD) to be at least 1%. ALSPAC is an anonymous study, and hence seropositive children could not be individually identified or undergo biopsy. Inasmuch as all children within ALSPAC suspected of having CD are referred to just 1 center, we aimed to identify children with biopsy-confirmed CD who were likely to be in this cohort and to estimate the magnitude of discrepancy between serology-positive cases and biopsy-confirmed cases. The results suggest that more than 90% of CD in children goes undiagnosed.