The white blood cell count (WBC) at admission correlates with prognosis in septic shock. It is not known if the WBC trajectory impacts survival. We used trajectory analysis to study the WBC over 7 days of ICU admission. We developed a multinomial logistic regression model to evaluate the patient and illness factors with WBC trajectories. We constructed a multivariable Cox proportional hazard models to evaluate the association of WBC trajectory on 30-day mortality. The favored model identified seven WBC trajectories. We found that platelet count and sex were associated with WBC trajectory. In a multivariable Cox proportional hazard model, group 5 (rising WBC) was associated with increased hazard of death (HR 3.41 (95% CI 1.86 to 6.26), p<0.01). We found seven unique and clinically relevant groups of patients. Routine baseline characteristics are poor predictors of trajectory group assignment. The rising WBC trajectory is associated with an increased risk of death.