Young people in Mongolia are growing up in an era of profound political, economic and cultural changes. The period of adolescence is also lengthening as biological maturity is reached earlier but the social and economic independence necessary for marriage is reached later. Sexual activity among adolescents is probably becoming more common though rather little secure evidence is available. The aim of the study was to develop a body of knowledge that will assist to: (i) identify the main sexual health information needs of secondary school students; (ii) create the necessary knowledge base for appropriate policies and programmes, with particular attention to in-school sexuality education. The study combines quantitative and qualitative approaches to examine the sexual conduct of secondary school students in Ulaanbaatar. Data were collected on: i) sexual beliefs and practices that are common among young people, ii) their perceived concerns and needs, and iii) views of relevant 'stakeholders' - teachers, doctors. and parents - with regard to sexuality of young people and their sexual information needs. A sample of 2,028 students aged 14-18 years was drawn from 22 schools in the capital city. A self administered questionnaire was used to elicit knowledge, attitudes and behaviours. In addition, 41 in-depth interviews and 13 focus group discussions were conducted. The results show that young people are exposed to health hazards through their sexual behaviour, and that they would welcome and benefit from school-based sexuality education. Most 'stakeholders' had limited knowledge about the sexuality of adolescents but a large majority considered that sex education should be included in school curricula.