Idiopathic granulomatous hypophysitis is a rare inflammatory disease of unknown aetiology; few cases are reported. We review the clinical presentation and radiological characteristics of these cases and our own experience with three new surgical cases, to determine diagnostic criteria. MRI of three cases revealed sellar lesions extending into the chiasmatic cistern. Their shape varied, from dumbbell to spherical and elliptical. All were isointense with the brain on T1-weighted images and gave heterogeneously high signal on T2- weighted images. Contrast enhancement was homogeneous in one case and heterogeneous in another. The pituitary stalk could not be identified. There was no dural enhancement. The sphenoid sinus mucosa was thickened in two cases and normal in one.