In the last 20 years, there has been a dramatic upsurge in the average weight of Australian adults. In this period, on average, Australian women have gained 4.8 kg, whilst Australian men have gained 3.6 kg. Consequently, the prevalence of obesity in men has increased from 8% to 19% and in women from 7% to 21%. This threatens to wipe away many recent health gains, as obesity has been associated with a wide range of chronic and debilitating illnesses, such as diabetes, heart disease, some cancers, sleep apnoea and osteoarthritis. Any weight gain in adulthood is usually as a result of an increase in fat stores, and the risk of ill-health from increasing weight actually begins at quite low BMI. Unfortunately, weight gain can be difficult or slow to reverse in the middle years because of physiological and behavioural changes that occur at this time of life. Adults should focus on preventing or minimizing weight gain over time by retaining physical activity within their daily living and by sensible dietary changes. Even if weight gain does occur with age, a regimen of regular exercise and a diet rich in fruit and vegetables and low in fat will provide some protection against a rapid decline in health.