We hereby report a case of a 62-year-old male patient who was misdiagnosed with adrenal insufficiency during the course of protein-losing enteropathy caused by superior mesenteric arterial thrombosis. The patient was suspected to have adrenal insufficiency due to hyponatremia and severe weakness. The cortisol responses to the initial challenge of 250microgram ACTH were inadequate (maximum serum cortisol level after ACTH challenge was 10.9microgram/dL), while the serum albumin concentration was 1.9g/dL. Subsequently, intravenous steroid therapy was given to the patient. However, after bowel resection, the serum albumin level increased to 3.4g/dL and the cortisol response to the follow-up rapid ACTH stimulation was completely normal. Accordingly, we discontinued steroid replacement and discharged the patient without any problem. In conclusion, measuring total serum cortisol in a patient with hypo-pro-teinemia may lead to misdiagnosis of adrenal insufficiency. In such cases, caution should be exercised in interpreting the results in terms of total serum cortisol level or measurement of serum free cortisol levels should be considered.