Data concerning 19 health-related behaviours and associated beliefs were collected by questionnaire from 282 students in the Netherlands on two occasions over one year. While all behaviours showed moderate stability, there were variations in the degree of change. The highest stability was reported for sleep time, tooth brushing frequency, seat belt usage and health care service utilization. The least stable behaviours included regular exercise and various dietary measures. Predictors of changes in smoking, dietary fat intake, alcohol consumption and regular exercise were analysed in detail. Beliefs assessed at year 1 in the importance of these activities for health predicted changes in behaviour over the study year independently of prior be...