Thiamine is an essential co-factor for aerobic metabolism. Both thiamine deficiency and sepsis may be associated with hyperlactatemia and hypotension. We assessed the relationship between thiamine compounds, lactate concentrations and clinical outcomes in septic patients.We undertook a prospective observational single-center study. Erythrocyte levels of total thiamine, free thiamine, thiamine mono, di and triphosphate (TMP, TDP, and TTP respectively), the erythrocyte transketolase activity (ETKA) and the effect of thiamine diphosphate on ETKA were measured in septic patients by high performance liquid chromatography and correlated with arterial lactate. Vital status at the end of intensive care unit stay was recorded.Overall, 28 patients suffering from sepsis were included. Median (interquartile range [IQR]) age was 60 [44-77.3] years, 15 (53.6%) patients were male, median [IQR] simplified acute physiology score II was 40 [27-50]. There was no correlation between total thiamine and lactate levels (P = .33). There was no correlation between free thiamine (P = .81), TMP (P = .71), TDP (P = .31), TTP (P = .86), and lactate levels in our population. There was no correlation between ETKA (P = .58) or the effect of TDP on ETKA (P = .40) and lactate concentration. Total thiamine and TDP concentration were significantly higher in intensive care unit (ICU) survivors than in nonsurvivors (P = .03 and P = .03). The effect of TDP on ETKA was significantly higher in nonsurvivors compared to survivors (P = .04).We found no correlation between thiamine compounds and lactate concentration in sepsis. Thiamine deficiency in sepsis may be associated with ICU-mortality.