Diaphragma sellae meningiomas are unusual tumours often not distinguished from pituitary macroadenomas. Preoperative differentiation is essential, because the trans-sphenoidal approach is used for surgical removal of adenomas, while meningiomas are approached via a craniotomy. We reviewed five patients in whom a diaphragma sellae meningioma was initially diagnosed as a nonsecreting pituitary macroadenoma. MRI criteria for differential diagnosis are discussed. The main findings considered are visibility of the pituitary gland, contrast enhancement, the centre of the lesion and sellar enlargement. These criteria, applied to a blind review, allow correct identification of the tumours.