Objective: to determine the preponderance of ideas in adolescents about the relationship between maternal habits and the health of the fetus. Design: quantitative survey using a preceded questionnaire, the content of which was derived from the transcripts of interviews and the responses to open-form questionnaires. Setting: North West Region Health Authority area, UK. Participants: 674 adolescents in British National Curriculum Year 10 (age 14/15) from 6 Community Comprehensive Schools. Findings: most of the adolescents were aware of the dangers to the fetus of alcohol and smoking, including passive smoking. However, they were less aware of the potential hazards during pregnancy of eggs (Salmonella), soft cheeses (Listeria), liver (Vitamin A excess) or handling cats (Toxoplasmosis). Most of the respondents thought that the optimum time to initiate actions for a healthy pregnancy was when pregnancy had been confirmed, suggesting that the benefits of preconceptual care are not well known. Key conclusions: adolescents lack knowledge about some of the specific hazards to the fetus of maternal diet and behaviour during pregnancy and are unaware of the importance of the early stages of pregnancy in this context. Implications: there is a need for the provision of education about the importance of a healthy maternal lifestyle before conception and during early pregnancy for adolescents. Midwives may have a proactive role in such education, but should be aware that young people may have specific areas of ignorance and misconceptions which will need addressing.