Isolated ACTH is a rare cause of secondary adrenocortical insufficiency. The diagnosis is made by the demonstration of low cortisol production with low plasma ACTH, absent adrenal responses to stimulation for pituitary or hypothalamus with intact adrenal response to exogenous ACTH, and normal secretory indices of other pituitary hormones. We conclude that the diagnosis of this condition may be difficult due to the varied clinical presentation and etiologies.