Summary: Lactose intolerance is an important problem in pediatric and gastroenterological practice, causing abdominal pain, bloating and diarrhea after milk or milk-containing product consumption. Differentiation between lactose intolerance, lactose malabsorption and lactase deficiency is an important issue. There are four clinical situations: acquired primary lactase deficiency, congenital lactase deficiency, developmental lactase deficiency and secondary lactose malabsorption. It is important to distinguish between lactase deficiency and symptoms of small intestinal bacterial overgrowth and functional disorders of the gastrointestinal tract in differential diagnosis. Beyond clinical features, there are stool analyses, the lactose breath hydrogen test, small bowel biopsy and genetic tests in the diagnostic approach. The goal of lactose intolerance management is to deal with the symptoms by limiting the consumption of lactose-rich foods in the diet.