: Rathke's cleft cysts (RCCs) are non-neoplastic, sellar or suprasellar epithelium-lined cysts originating from Rathke's pouch in the pituitary gland. Patients with RCCs are usually asymptomatic, but some have only been identified when symptoms manifested in middle age. The characteristics of these patients during childhood or adolescence remains unknown. We describe an 18-year-old girl who had occasionally suffered from malicious fatigue in the morning since her early teens. Brain magnetic resonance imaging (MRI) revealed T1 hyperintense/T2 hypointense signals between the anterior and posterior pituitary glands, indicating the presence of RCC. Based on an authentic endocrinological evaluation, her adrenal function seemed normal; nevertheless, her serum cortisol level strangely dropped around noon. Furthermore, daily supplementation of oral hydrocortisone bizarrely suppressed ACTH secretion to below the detection range in the morning. These data appeared compatible with the presence of central adrenal dysfunction. We also review the literature for previously reported cases. In conclusion, the symptoms and endocrinological data for dysfunction of the hypothalamic pituitary system might be non-specific and vary among patients, especially in teenagers. Brain MRI and daily cortisol profiling in blood are key to obtaining a diagnosis of an impaired hypothalamic adrenal function due to RCC.