Cushing's syndrome is a potentially lethal or invaliding condition wit
h a cure rate higher than 80%, if adequate diagnostic and therapeutic
procedures are applied. Diagnostic imaging of pituitary and adrenals (
CT, NMR, sonography) discloses only weak evidences of the origin of hy
percortisolism, but definite diagnosis is obtained by endocrine testin
g in more than 95% of the patients. Test procedures may be confused by
a cyclic occurrence of hypercortisolism, the intake of antiepileptics
, tuberculostatics or synthetic glucocorticoids and by problems during
sample processing for ACTH measurement. Known causes for falsely posi
tiv or negative results of standard endocrine tests are described.