Psychosocial variables associated with health-related behaviours for diet, physical activity, alcohol consumption and smoking were examined in 18 year-old Australian men (n = 301) and women (n = 282). These psychosocial variables included Type A behaviour and depression, perceived self-efficacy for engaging in healthy behaviours and perceived barriers to performing these behaviours. Self-efficacy for following a healthy diet and moderating alcohol intake was greater in females but males had higher self-efficacy for physical activity. Self-efficacy for smoking did not differ according to gender. Lack of willpower was perceived as a barrier to desirable dietary, smoking and physical activity behaviours. Other perceived diet-related barriers included buying suitable foods when eating out, ignorance about appropriate foods and, in young women, perceived expense. Barriers for desirable levels of physical activity included planning time, tiredness, limiting social life and lack of social support. Social occasions were the main perceived barriers preventing both alcohol moderation and quitting smoking. Lack of family support, stress and concerns about weight gain, particularly in women, were perceived barriers to smoking cessation. Type A behaviour was associated with smoking and "unsafe" drinking in both men and women, generally unhealthy dietary choices in young women but with greater physical activity in young men. Depressive affect was significantly higher in female smokers and "unsafe" drinkers and tended to have an inverse relationship with physical activity in men and women. Depressive affect was inversely related to self-efficacy in both men and women for each of the health behaviours examined. Health promotion in young adults should therefore attempt to increase self-efficacy and address perceived barriers to change, taking into account gender-related differences in attitudes and the influence of depression and Type A characteristics on health-related behaviours.