Objective: To study the effect of increased folic acid intake on the prevalence of neural tube defects (NTD) in The Netherlands. Study design: Using the capture–recapture method, the prevalence of NTD was estimated on the basis of five different registries on births affected by NTD. Results: Total prevalence over the 1988–1998 period varied between 1.43 and 1.96 per 1000 live and still births. No decrease in total prevalence was found to have taken place during that period. Scrutiny of the last 2 years, 1997 and 1998, in which increased folic acid intake might be expected to have had an effect, did not give any indication that the prevalence of NTD was falling. Conclusions: A decrease in the Dutch prevalence of NTD during the study period could not be demonstrated due to the relatively small number of women using folic acid periconceptionally. This does not mean automatically that periconceptional folic acid use is ineffective in reducing the Dutch prevalence of NTD. Further monitoring is needed.