Background. To decrease the risk of neural tube defects, all women planning pregnancy or capable of becoming pregnant should take folic acid supplements. The aim of the study was to describe the association between pregnancy planning and vitamin supplement use. Methods. A total of 1,858 pregnant women registered for a prenatal ultrasound examination in the Montérégie region, Province of Quebec, Canada, completed a questionnaire between November 1997 and May 1998. Pregnancy planning was described by six ordinal variables, which were included in a nonlinear principal component analysis. The main dimension representing the intensity of pregnancy planning was used as the dependent variable in a multivariate linear regression model, and as a basis for assessing vitamin use according to four levels of planning. Results. A majority of women scored high for intensity of pregnancy planning. Planning intensity score increased with age and was higher among women who attended university, had a family income greater than CAD $30,000, and were married. Vitamin use in the period prior to conception occurred with a frequency of 27.5%, increasing moderately with planning intensity scores. Overall, only 13.5% of fetuses were exposed to adequate doses of folic acid. Conclusion. A promotion campaign selectively targeting women likely to plan a pregnancy could have a significant impact in reducing neural tube defect incidence.