Asthma and gastro-oesophageal reflux are both common medical conditions and often co-exist. Studies have shown conflicting results concerning the effects of lower oesophageal acidification as a trigger of asthma. Furthermore, asthma might precipitate gastro-oesophageal reflux. Thus a temporal association between the two does not establish that gastro-oesophageal reflux triggers asthma. Randomised trials of a number of treatments for gastro-oesophageal reflux in asthma have been conducted to determine whether treatment of reflux improves asthma.