Background: Previous trials evaluated the incidence of critical illness-related corticosteroid insufficiency (CIRCI) using 250 μg adrenocorticotropic hormone (ACTH). However, this supraphysiological dose could result in false-positive levels. We aimed to determine the incidence of CIRCI in septic patients using a 1 μg ACTH stress test. Methods: We conducted a prospective cohort study on 39 patients with septic shock. Critical illness-related corticosteroid insufficiency was defined as a Δ max cortisol <9 μg/dL after 1 μg ACTH stress test. The primary outcome of the study was death. Secondary outcomes included days of vasopressors, days of mechanical ventilation (MV), amount of fluid per day, the incidence of acute kidney injury (AKI), and days of intensive care unit (ICU) stay. Results: The incidence of CIRCI in our cohort was 43.6% using 1 μg ACTH. There were no significant differences between groups in terms of ICU scores, laboratory investigations, vasopressors, MV days, amount of fluid per day, and the ICU stay ( P = > 0.05). The CIRCI group had lower median survival and survival probability rates (5 days and 48.4%, respectively) compared with the non-CIRCI group (7 days and 49.5%, respectively). In addition, the CIRCI group had a shorter time to develop AKI and a higher probability of developing AKI (4 days and 44.6%, respectively) in comparison with the non-CIRCI group (6 days and 45.57%, respectively). Conclusion: We concluded that the CIRCI group had a lower mean survival rate and a higher incidence of AKI. We recommend the use of 1 μg ACTH test in septic shock patients to identify this subgroup of patients.