The article presents a clinical case of observation and treatment of a patient with late-onset Pompe disease (LОPD), a rare hereditary storage disease associated with a deficiency of the enzyme acid maltase (acid α-glucosidase) in lysosomes. The first signs of the disease in patient S. – recurrent abdominal pain – appeared at the age of 10. The diagnosis of late-onset Pompe disease was made in one of the federal centers after careful laboratory and molecular genetic studies. Enzyme replacement therapy with Alglucosidase Alpha gave positive results: the patient's condition stabilized, the activity of a number of indicators decreased – aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine phosphokinase (CPK). The presented proven clinical case of late-onset Pompe disease with an assessment of the patient’s condition before treatment and the results after enzyme replacement therapy can be useful in the practical work of a wide range of doctors - internists, gastroenterologists, neurologists, general practitioners, etc.