Three hundred and ninety-one adolescent Western Australians, mean age 15.8 years, completed questionnaires to determine nutritional knowledge and behaviours including stage of change; health beliefs and values; barriers to change; self-efficacy; locus of control; dietary patterns; alcohol and smoking habits; television-watching; weight, height and body image. Highest ranking beliefs and values regarding healthy diets were improving health, feeling energetic, feeling good about oneself, controlling weight, lowering cholesterol, testing willpower and improving appearance. Important barriers to healthy eating were lack of suitable foods at home and school, inability to influence food choices at home, and ignorance about nutrients. Nutritional knowledge, particularly concerning fat, was deficient. Healthy eating related negatively to television watching and alcohol, and positively to self-efficacy, nutrition knowledge, considering weight control and well-being as important, and having influence over foods at home. Of the 28% of boys and girls who drank alcohol, 20% reported intake above 'safe' limits. Twenty-four percent of boys and 22% of girls smoked. Fifty-four percent of girls and 21% of boys considered themselves overweight including 20% of the leanest girls and 8% of the leanest boys. Nutrition education for adolescents should incorporate self-efficacy, relevant health values and barriers-to-change, education about nutrients, and improved access to healthy foods. Adolescent smoking and drinking should also be targeted.