Population-based screening studies have documented prevalence of celiac disease (CD) at 1% at age 7 years, but 90% of children remain undiagnosed. This prospective cohort study aims to examine whether observed differences in diagnosis rates of CD exist between children from different socioeconomic groups and how this has changed over a 12-year period. All children aged ≤15 years with a postcode within South West of England (SWE) diagnosed with CD during a 12-year period (1999-2010) when all diagnoses were based on endoscopic histology were included in the study. The incidence rates in socioeconomic groups were determined using the Index of Multiple Deprivation Score and Office of National Statistics population data. Four hundred fifteen children were diagnosed with CD; 65 withinthe City of Bristol (CoB). Diagnosis rate rose 4.2 times in SWE and 3.1 times in CoB between the first and last 4 years of the study. The rate was 1.6 times higher in the least socioeconomically deprived compared to most deprived (2.2 times in CoB), and the gap widened over the 12 years. Missed cases estimates for CoB and SWE are at least 83% and 91%, respectively.Conclusion: These findings suggest that while incidence of diagnosed CD in children has increased over a 12-year period, 83-91% remained undiagnosed. Socioeconomically deprived children are more likely to be underdiagnosed, and the gap between the least and most deprived has widened. To fully address massive underdiagnosis, further strategies including pilot studies using finger prick serological mass screening for CD in children entering primary schools are needed. What is Known: • Epidemiological studies record a 1% prevalence of celiac disease (CD), but up to 90% of children may remain undiagnosed. • Previous studies have documented an increased incidence of CD in higher socioeconomic groups, but proposed reasons remain conflicting. What is New: • Incidence of diagnosed CDhas gone up across all social classes but more so in higher socioeconomic groups and there is an increasing health/wealth gap. • This study estimates that 83-91% of children with CD are still being missed despite improved and easily available serological testing and suggest that population screening should be reconsidered.