Summary: Lactose intolerance is a disease that can reduce the patient's quality of life. Patients complain of abdominal pain, flatulence and diarrhea. These symptoms are not specific, therefore the disease requires differentiation with many diseases. Sometimes lactose intolerance is a manifestation of a different disease than primary adult lactose deficiency. Information in which the patient states that the symptoms occur after the consumption of dairy products raises the suspicion of lactase deficiency, the enzyme responsible for the breakdown of lactose. The most commonly used lactose breath test is used for diagnosis. In the treatment of the disease, a lactose-restricted diet is recommended. Another highly effective method of treatment that allows for less dietary restrictions is the supplementation of the lactase enzyme with meals containing dairy products. The therapy may be supplemented by the use of probiotic strains that will beneficially modify the colon microbiome.