Introduction: The pornography industry is a pervasive influence on adolescents, nearly all of whom are exposed to it via the internet, either willingly or unwillingly and at a more or less premature age. Is there an association between exposure to pornography and some forms of risk behaviour? Method: Eight hundred and twelve Lille students responded anonymously to a questionnaire given to them on the occasion of a consultation at a health centre. Logistic and linear regressions were used for statistical analysis. Findings: Nearly all men and 80% of women had been exposed to pornography. The average age of initial exposure was 15.2 years. Exposure at a premature age is associated with sexual activity at a younger age and with a greater inclination to seek out casual partners and use cannabis more frequently. The age of exposure does not on the other hand appear to have any influence on the number of sexual partners, the practice of anal penetration, alcohol or tobacco consumption, contraceptive use and taking risks in terms of sexually transmitted infections. Frequent viewing of pornographic images is associated with sexual activity at a younger age, a larger number of sexual partners, an inclination to seek out casual partners, the practice of anal penetration, a lower level of prevention of sexually transmitted infections and unwanted pregnancies and finally, a higher consumption of alcohol and cannabis. In conclusion, these findings should be taken into account, and should lead those involved in sexual health and sex education to increase the amount of information they provide to adolescents.