Fructose exists in food naturally or as a sweetening additive. It has been thought that fructose malabsorption may cause the gastrointestinal symptoms seen in patients with irritable bowel syndrome. However, fructose malabsorption is still poorly understood, and clinicians are still uncertain of its role. This review attempts to clarify the relation between fructose malabsorption and symptoms in normal individuals and patients with irritable bowel syndrome. The main problem lies in the diagnosis. First, there is no definite cut off value for the breath tests. Second, we are unsure of the normal absorptive capacity of fructose in normal individuals. Normal individuals will have a degree of fructose malabsorption with or without symptoms depending on the dose of fructose used. From earlier studies, 25 g of fructose seems to be the cut-off dose to investigate fructose malabsorption, with a positive breath test at this dose suggesting abnormally low capacity to absorb fructose. This low level may be difficult to exclude from the daily diet, resulting in symptoms of fructose malabsorption.