BACKGROUND: In the setting of severe sepsis and septic shock, mortality increases when lactate levels are ≥ 4 mmol/L. However, the consequences of lower lactate levels in this population are not wel understood. The study aimed to determine the in-hospital mortality associated with severe sepsis and septic shock when initial lactate levels are < 4 mmol/L. METHODS: This is a retrospective cohort study of septic patients admitted over a 40-month period. Totally 338 patients were divided into three groups based on initial lactate values. Group 1 had lactate levels < 2 mmol/L; group 2: 2–4 mmol/L; and group 3: ≥ 4 mmol/L. The primary outcome was in-hospital mortality. RESULTS: There were 111 patients in group 1, 96 patients in group 2, and 131 in group 3. The mortality rates were 21.6％, 35.4％, and 51.9％ respectively. Univariate analysis revealed the mortality differences to be statistically significant. Multivariate logistic regression demonstrated higher odds of death with higher lactate tier group, however the findings did not reach statistical significance. CONCLUSION: This study found that only assignment to group 3, initial lactic acid level of ≥ 4 mmol/L, was independently associated with increased mortality after correcting for underlying severity of illness and organ dysfunction. However, rising lactate levels in the other two groups were associated with increased severity of illness and were inversely proportional to prognosis.