Various aspects of the neurocognitive consequences of hypercortisolism have been studied in recent years. However, a major limitation of most previous studies is the small sample size. Longitudinal research data is sparse. A further limitation is that CS is a heterogeneous disease with several etiologies, varied clinical findings at presentation and varying outcome after treatment. Consequently, and since CS is a rare syndrome, the number of patients needed to be studied is too large for a single center. A collaborative multi-centre effort is therefore a desirable approach.