Objective: To assess the relationship between high intake of folic acid and positional plagiocephaly. Design: Retrospective case-control study with questionnaires administered in the clinic to biological mothers of children with positional plagiocephaly (PP group) and mothers of children without it (CO group). Setting: Tertiary, institutional clinic. University Hospital of Maastricht, The Netherlands. Patients, Participants: Exclusion criteria: mothers of children with syndromic disease or bone deformation and of children with clearly continuous forces on the skull (torticollis). A total of 94 mothers were included in the PP group (response rate: 85%), and 74 were included in the CO group (response rate: 75%). Final sample sizes were 75 in the PP group and 54 in the CO group. Main Outcome Measures: The recommended daily dosage of folic acid in The Netherlands is 400 mu g. The primary outcome was folic acid dosage in relation to the recommended dosage. A secondary outcome was duration of folic acid intake in relation to the recommended period of use during pregnancy. Results: In the PP group, 20% used double the recommended dosage of folic acid, compared with 6% in the CO group (p <.05). In the CO group, 59% used folic acid longer than recommended compared with 56% in the PP group (not significant). There were no differences in baseline characteristics except for gestational period: 39.5 weeks in the PP group and 37.9 in the CO group (p <.05). Conclusion: Excessive daily intake of folic acid during pregnancy is seen among mothers of positional plagiocephaly patients.