Introduction and purpose: Thiamin (Vitamin B1) is a water-soluble vitamin. It plays an important role in many biological processes, mainly in glucose metabolism. Its deficiency is called beriberi disease. Beriberi was discovered at the turn of the 19th and 20th centuries and is now a disease that occurs in both underdeveloped and highly developed countries. Brief description of the state of knowledge: Thiamine deficiency can affect the cardiovascular, nervous and immune systems, which is seen as dry, wet, fulminant beriberi or as Wernicke-Korsakoff syndrome. Worldwide, vitamin B1 deficiency is most commonly reported in populations where rice and ground grains are the main food source, but also in patients with chronic alcohol abuse, diabetes, gastrointestinal surgery, cancer, and patients undergoing chronic diuretic therapy, which increases urine loss. Summary: Treatment of beriberi disease consists in supplementing vitamin B1 in appropriate doses. The symptoms of thiamine deficiency are non-specific, however, early diagnosis and initiation of vitamin administration quickly lead to clinical improvement. It should be remembered that thiamine deficiency is often not included in the differential diagnosis of complaints reported by patients. This may be due to the belief that diets in European countries containing food products enriched with vitamins exclude clinically evident micronutrient deficiencies.