The aim of this study is to find out how much young people know about the harmful effects of intoxicating substances have on foetus during pregnancy. The aim of this study is to find out if young people need more information on the subject. This is a quantitative study. The material was collected using questionnaire forms. 48 students aged 16-18 from Suolahti Upper Secondary School and Catering College of Jyväskylä Vocational Institute participated in the inquiry that was carried out in February 2006. The material was analysed using Microsoft Excel software. According to the study results the students that participated in the study generally knew that it is not advisable to use intoxicating substances during pregnancy. However, they need more specific information on the harmful effects that using intoxicating substances has on foetus. Most of the students thought that you can continue smoking cigarettes until thepreganancy is tested. Half of the students did not know the harmful effects of second-hand smoking for foetus. The students were uncertain about the effects of alcohol in early stages of pregnancy. Most of the students thought that using alcohol becomes harmful only after the pregnancy has been tested. More than half of the students thought that drinking beer or cider during pregnancy is safer than drinking strong alcoholic drinks. The students answered better to questions concerning narcotic substances than to questions about smoking cigarettes and drinking alcohol. The majority of the students participating in the study knew that using drugs can damage foetus and cause deformities.