Thiamine or vitamin B1 is a water soluble vitamin of the vitamin B complex. It is synthetized by bacteria, fungi and plants and is an essential component of multicellular living organisms. Humans are not able to synthetize this vitamin and have to obtain it from different foods. Thiamin has a vital role in the normal function of the human body. It functions as a coenzyme in the catabolism of carbohydrates and amino acids and has an antioxidant role. It has an essential function in a series of metabolic processes related to energy production and conversion of sugar to ATP, as a catalyst in the Krebs cycle. It takes part in the synthesis of neurotransmitters and has a main role in the central nervous system and immune system. Deficiency results in Wernicke-Korsakoff syndrome, optic neuropathy, Beri-Beri and other disorders. Vitamin B deficiency in not rare and may occur in conditions related to malnutrition, alcoholism, diabetes, congestive heart failure and others. In this review an effort has been made to demonstrate the presence of thiamine deficiency in various clinical situations frequent in modern medicine, attributed in the past to populations with "classical" inadequate feeding and starvation, or severe malnutrition. Identification of potential causes of vitamin B1 deficiency, knowledge of its metabolic properties and the clinical manifestations of its deficiency are important for the implementation of early therapeutic response required for the reduction and prevention of symptoms related to this disorder.