Increases in both overweight and life expectancy of the population will lead to a larger number of patients with knee problems due to osteoarthritis (OA). Several changes, metabolic as well as functional, link obesity with OA. Randomised controlled trials have shown substantial and clinically relevant disability and symptom relief in obese patients with knee OA following moderate weight loss. While exercises are good for the functional status in general, it is advisable initially to prescribe weight loss as therapy of patients with a combination of obesity and OA.