Disaccharide intolerance presents a pathogenic heterogeneous and most complex clinical entity. It usually occurs due to primary or secondary deficit of disaccharide activity, and rarely because of disorders of absorption or monomer metabolism. Symptomatology of disaccharide maldigestion and/or malabsorption depends on the severity of the basic disorder, the level of its overload and the patient’s age. In the youngest children, due to a rapid gastrointestinal transit and a low compensatory capacity of the colon, osmotic-fermentative diarrhoea forms the basis of clinical features. Diarrhoeal disorder can be occasionally so intensive that it disturbs not only water and electrolytic balance, but also the nutritive status of the child. In older children and adults, as well as in milder forms of the disorder, the symptomatology, most often without diarrhoea, is dominated by abdominal colic, loud peristaltic sounds, meteorism and increased flatulence. Metabolic disorders followed by conversion disorders of galactose and fructose into glucose are characterized by a hypoglycaemic crisis, as well as by various multisystemic damages due to the deposit of toxic metabolic products. The diagnosis of gastrointestinal forms of disaccharide intolerance is based on the pathologic clinical and laboratory response during the overload test, while that of the metabolic form is based on the confirmed presence of specific enzyme and/or genetic defect. Treatment of disaccharide intolerance is based on the elimination diet. Besides, in the secondary forms of the disorder, it is also necessary to apply the treatment of the basic disease.