Cardiovascular disease (CVD) and cancer are major causes of death for women, and osteoporosis negatively impacts upon the health and quality of life of many older women. There is evidence that risk of developing these diseases is partially determined by lifestyle factors, such as physical activity, diet and smoking, as well as being influenced by hormonal changes during the menopause. Participation in preventive strategies will be influenced by women's perceptions of the relative risks of developing these diseases, and beliefs about the effectiveness of the particular strategy. In this study, 103 mid-aged women were asked about their health and health behaviours and to estimate: (1) their future likelihood of developing CVD, osteoporosis and breast cancer; and (2) their future likelihood of developing diseases (a) if they improved their health behaviours, and (b) if they used hormone replacement therapy (HRT) for 5 years. Women believed that improving their health behaviours (diet, physical activity, smoking) would reduce their risks of CVD and osteoporosis, although modest reductions were expected. Breast cancer was not seen as significantly modifiable by lifestyle changes. They believed that taking HRT would significantly reduce their risk of osteoporosis, increase their risk of breast cancer, but not alter their risk of developing CVD. The findings are considered in the context of health psychology models of behaviour change and have implications for health promotion for mid-aged women.