The incidence of positional plagiocephaly (PP) has increased during the last 2 decades in the Netherlands. Although this is generally solely attributed to the advice to put babies on the back during their sleep, other factors might be of influence. Because the advice to take folic acid (FA) was initiated in the same period as the sleeping advice, this study was undertaken to evaluate the effect of FA on PP. It is known that a daily intake of 400 microg of FA around the time of conception is advised in periconceptive women to prevent development of neural tube defects. The maximal daily dietary folate intake is considered to be 250 mg with a bioavailability of 50% to 70%. However, periconceptional women may take a multivitamin containing pteroylmonoglutamine in addition to a FA supplement (isolated pteroylmonoglutamine). Therefore, the daily intake of FA will exceed 1 mg daily, which is considered the upper limit of daily folate ingestion. Data from the "Maastricht Cohort and Intervention study about pregnancy related girdlepain" were used to study the amount of folate containing supplemental intake of all the 7526 women. In this study, women were prospectively questioned about their FA intake. The entire cohort, considered the control group, was compared with a subgroup of women within this cohort with children with PP, treated by a plastic surgeon, considered the PP group. Double use, defined as isolated FA preparations in addition to folate containing supplements (vitamins), was seen more frequently in women giving birth to children with PP. In the PP group, double use was seen in 33.3% of the women compared to 13.2% in the control group. Although no statistical analysis could be made because the PP group was too small, the use of too high dosages of FA might have an adverse effect in causing more PP. This article does not want to discuss the beneficial effect of FA during pregnancy. However, we observed a potential empirical relation between PP and FA double intake requiring attention in more extensive studies.