The clinical significance of subclinical Cushing syndrome has been widely recognized because of its high prevalence in adrenal incidentaloma. Circulatory and metabolic disorders are the most frequent and important complications of the disease state. Since those complications show aggravation during the clinical course and improvement after surgery, appropriate diagnosis and treatment are essential. Diagnostic criteria, especially the cutoff value of plasma cortisol after dexamethasone suppression, are markedly affected by the sensitivity and specificity of cortisol assay methods. Revision of the diagnostic criteria should reflect the prognosis of the disease state.