Monitoring in the setting of critical illness must be linked to beneficial therapy to affect clinical outcome. Elevated serum lactate is associated with an increase in mortality in emergency department (ED) patients with severe sepsis and septic shock. The reduction of lactate levels toward normal during acute resuscitation is associated with improved clinical outcomes. The majority of data demonstrating the interventions used to achieve a reduction in lactate levels and the associated clinical outcomes have been obtained during protocolized randomized trials. We therefore conducted a retrospective observational cohort study of 243 adult patients with severe sepsis and septic shock to assess the interventions associated with nonprotocolized serial lactate monitoring and to assess clinical outcomes. A multivariable model was used to assess outcome differences between the serial lactate (SL) and no serial lactate (NL) cohorts. The SL group received more crystalloid resuscitation (3.6 L vs. 2.5 L; P < 0.01), central venous oxygen saturation monitoring (30% vs. 12%; P < 0.01), and central venous pressure monitoring (23.5% vs. 11.8%; P = 0.02). By day 28, a total of 31 patients in the SL group (23.5%) and 44 in the NL group (39.6%) had died. Multivariable logistic regression analysis demonstrated that the lack of serial lactate monitoring was independently associated with mortality (adjusted odds ratio, 2.09; 95% confidence interval [CI], 1.12 – 3.89; P = 0.02). The SL group also showed greater improvement in 24-h Sequential Organ Failure Assessment scores (1.16 vs. 0.19; P = 0.03), decreased intensive care unit length of stay in days (4.6 vs. 6.0; P = 0.04), and more ventilator-free (19.9 vs. 16; P = 0.05) and vasopressor-free (21.6 vs. 17.9; P = 0.02) days. In the setting of routine clinical care, serial lactate monitoring is associated with an increase in crystalloid administration, resuscitation interventions, and improved clinical outcomes in ED patients with severe sepsis and septic shock. This suggests that serial lactate monitoring, targeting a reduction in lactate levels to normal, is a generalizable resuscitation target in the ED.