PIP: This review of the literature and current knowledge concerning a nutritional disorder of disaccharidase deficiency discusses the following topics: 1) a description of disorders of disaccharide digestion; 2) some historical perspective on the laboratory and bedside advances in the past 10 years that have helped define a group of these digestive disorders; 3) a classification of conditions causing disaccharide intolerance; and 4) a discussion of some of the specific clinical syndromes emphasizing nutritional consequences of these syndromes. The syndromes described include congenital lactase deficiency, acquired lactase deficiency in teenagers and adults, acquired generalized disaccharidase deficiency secondary to diffuse mucosal damage, acquired lactose intolerance secondary to alterations in the intestinal transit, sucrase-isomaltase deficiencies, and other disease associations connected with lactase deficiency such as colitis.