Background: Surveillance data from population-based congenital anomaly registers in 16 regions of Europe (mainly Western Europe) were analysed to assess the impact of the Chernobyl accident on the prevalence of selected congenital anomalies. Methods: Three cohorts of pregnancies were defined: those exposed during the first month following Chernobyl (External Exposure Cohort), the first year (Total Exposure Cohort) and the two subsequent years (Control Cohort). Expected numbers of congenital anomalies in these cohorts were calculated from 1980-1985 baseline rates. Registries were grouped into three exposure categories according to first-year exposure estimates. Results: There was no overall or dose-related increase in prevalence in the two exposed cohorts for Down's Syndrome, neural tube defects, other central nervous system defects or eye defects. There was a statistically significant overall 22% (95% CI: 13-31%) excess of Down's Syndrome in the Control Cohort, with no dose-response relationship. Conclusions: Chernobyl had no detectable impact on the prevalence of congenital anomalies in Western Europe, suggesting that in retrospect the widespread fear in the population about the possible effects of exposure on the unborn fetus was not justified. An increasing prevalence of Down's Syndrome in the 1980s, probably unrelated to Chernobyl, merits further investigation.