Multisystem inflammatory syndrome in children (MIS-C) is a disease related to coronavirus disease 2019 (COVID-19). Although the effects of COVID-19 on many systems are known, there is limited data regarding its effects on the endocrine system. This study aimed to discuss the effect of COVID-19 on cortisol dynamics in a patient who developed adrenal insufficiency after COVID-19 infection. An 11-yr-old boy with polymerase chain reaction-proven COVID-19 one month previously was referred with a five-day history of fever, vomiting, and rash. On admission, he had hypotension, tachycardia, and severe hyponatremia. After the evaluation, he was diagnosed with MIS-C and glucocorticoid therapy was initiated. During follow-up, the patient experienced adrenal insufficiency, and hydrocortisone treatment was initiated at a crisis dose. Four months later, the adrenal axis function had not recovered. The adrenocortical response in COVID-19 patients may be significantly impaired, resulting in increased mortality or morbidity.