Background: SARS-CoV-2, which emerged in China and spread globally, has been associated with adrenal insufficiency in numerous COVID-19 patients. The clinical evidence regarding adrenal involvement in COVID-19 patients is currently limited, primarily consisting of case reports and small patient series. Objectives: This study aimed to assess the variations in serum cortisol levels and evaluate the response of hospitalized COVID-19 patients to the adrenocorticotropic hormone (ACTH) test. Methods: This study was performed on patients with COVID-19 admitted to Valiasr Hospital, Birjand, Iran, in 2021. Sixty patients with COVID-19 were included in this study by simple random sampling. Patients' venous blood (5 mL) was collected in an EDTA anticoagulant tube. Blood samples were placed in a cool place, then 250 μg intramuscular cosyntropin was injected, and blood samples were taken again 60 minutes later. According to the kit protocol, cortisol levels were measured by a quantitative luminescence kit (Saluggia, Italy). Results: The study involved 60 participants, of which 32 were male (53.3%) and 28 were female (46.7%). The Mean participants' age was 63.1 ± 20.93. The median baseline cortisol serum levels were 28.075 µg /dL for men and 21.820 µg /dL for women. There was no significant difference between base cortisol serum levels (P-value = 0.248). After measuring the baseline cortisol levels in the studied patients, 21.7 % suffered from adrenal Insufficiency, 40 % were suspected of adrenal insufficiency and required cosyntropin injections, and 38.3 % did not have adrenal Insufficiency. Following the administration of cosyntropin injections, it was found that 33.3% of participants had adrenal insufficiency, while the remaining 66.7% did not exhibit any signs of adrenal insufficiency. Vital signs demonstrated that patients with adrenal insufficiency had notably lower mean systolic and diastolic blood pressures, and a statistically significant correlation was observed when comparing these two groups (P-value < 0.001 and P-value = 0.001, respectively). In assessing sodium and potassium serum levels between the two groups, individuals with adrenal insufficiency demonstrated lower average sodium levels (P-value < 0.001). At the same time, no noteworthy divergence was found in potassium levels between the groups (P-value = 0.587). Furthermore, no considerable discrepancy emerged in the in-hospital mortality rate during the patients' follow-up period (P-value = 0.322). As Adrenal insufficiency is life-threatening, early adrenal axis testing for COVID-19 patients with clinical suspicion of adrenal insufficiency should be carried out.