After describing the topographical anatomy of the pituitary gland, the sellar and parasellar region, in magnetic resonance (MR) imaging, the morphology of pituitary adenomas in MR imaging will be discussed and illustrated, with special reference to differential diagnostic aspects. The diagnostic information and the present clinical relevance of MR imaging, both in pretherapeutic and follow-up situations, will be considered. This will be done using unenhanced and gadolinium-enhanced T1-weighted spin-echo sequences in coronal as well as in sagittal cross sections at 1.5 tesla. Using MR imaging, questions of therapeutic significance concerning the definition of the tumor (evidence of its presence, size, the extent and the degree of infiltration) can be answered with greater precision. The procedure can be repeated with consistency. The contribution of magnetic resonance imaging to tissue characterization is limited. The latter requires consideration of the clinical symptoms and endocrine laboratory findings for differential diagnostic purposes. As disadvantages of MR imaging we should mention the exclusion of certain classes of patients (e.g. those with cardiac pacemaker), the limited potential for evaluation of the extent of invasion of the dura, poor visualization of calcification and insufficient recognition of changes in compact bone.