Background: Adults with intellectual disability have a range of significant health problems. If they are to live independently, they need to engage in behaviours that are health promoting, as well as avoiding behaviours that might directly lead to ill health. There is very little research about health-related knowledge and behaviour in this group. Method: A group of 38 adolescents with Down syndrome (DS) and their families participated in this study. A semi-structured interview and a series of tasks were used to collect data on individuals' health knowledge and behaviour relating to 4 aspects of health: hygiene, substance use, exercise and healthy eating. Results: While the majority of young people demonstrated some awareness of basic hygiene, they were not yet at the level where these behaviours could be guaranteed to occur without parental support. Knowledge about substance use, exercise and healthy food was generally poor. Conclusion: Knowledge of most aspects of health assessed in this study was poor and pointed to a gap in the preparation of these young people for independent living. (Contains 1 table.)