Tumour size on MRI (1.5T Siemens; slice thickness of 3 mm) was quantified by computerized measurements on coronal T1-weighted (TR/TE 650-800/20) contrast-enhanced images and a restricted field of view (20 ´ 20 cm), after identification of the tumor boun-daries by one neuro-radiologist (AMvdV). The major criteria used for pituitary adenoma detection on MRI were or no enhancement or delayed contrast enhancement after injection of gadolinium. MRI-images and PET-images were evaluated separately, each investigator being blinded for the results of the other technique.