This report presents the preliminary findings from WHO's (World Health Organization) fourth Health Behaviour in School-Aged Children (HBSC) Study. The study has two main objectives: (1) to monitor health-risk behavior in youth over time in order to provide the necessary background and clear targets for health promotion initiatives; and (2) to provide information to researchers that will enable them to understand and explain the development of health attitudes and behaviors through early adolescence. Approximately 1300 respondents in each of 3 age groups--11, 13, and 15 years--were targeted in 24 countries during the 1993-94 school year. The findings of the survey include: (1) in every country surveyed, the use of tobacco and alcohol increased with age; (2) in most countries, as young people progress from age 11 to 15, they exercise less frequently; (3) there is evidence to suggest that the diet of a significant number of young people in all countries does not conform to current nutritional advice; (4) in only one country, Sweden, did the majority of 11, 13, and 15 year olds rate themselves as very healthy; (5) in nearly all countries, only a small minority of students regularly felt lonely, helpless, or left out, while the majority thought they made friends easily, had at least two close friends, and found it easy to talk to their mother; (6) nearly 30 percent of the respondents reported an injury requiring medical attention during the previous year; this reaffirmed other research findings that unintentional injuries may be the most serious health problem to face school children in western societies; and (7) schools with a hospitable environment and caring teachers appear to contribute positively to students' emotional well-being and social development. Several implications for policy are included. Appendixes include: characteristics of countries, sample design and sampling error, a list of the principal investigators, and a list of HBSC publications. Contains 123 references. (AA)