Obesity has, among physicians, since long been considered to cause gastro-oesophageal reflux. The evidence in support of this belief has been scarce, however. During the last few years some population-based studies have addressed this clinically important issue. These studies demonstrated a clear and dose-dependent association between increasing degrees of overweight and gastro-oesophageal reflux. The mechanisms by which obesity causes reflux are unknown, although there is some limited data suggesting that hiatal hernia may be the causal link between obesity and reflux. Moreover, some evidence has been presented showing that obesity is clearly a stronger risk factor among women than among men, and that the relation between overweight and reflux is substantially augmented by postmenopausal hormone therapy. The data so far available point in the direction of oestrogens, the activity of which is strengthened by increasing body mass, being responsible for this effect. If the results are repeated in future studies, postmenopausal therapy might be avoided among obese females suffering from severe reflux. Weight-reduction seems to reduce the risk of symptomatic gastro-oesophageal reflux disease, indicating that such strategy might be a useful tool in the treatment of reflux.