Idiopathic orbital inflammation (IOI), formerly called orbital pseudotumor, is an orbital-specific disorder of unknown origin, characterised by an orbital mass consisting of nonspecific inflammation. It can affect any or all of the orbital structures, involving most frequently the lacrimal gland and extraocular muscles. Lacking pathognomic clinical and radiological features, IOI constitutes a diagnostic challenge as it is diagnosed by exclusion. In a clinicoradiologic context suggesting IOI, lesions of the lacrimal gland and orbital fat require biopsy to histologically confirm compatibility with IOI and exclusion of other disorders, where lesions of the extraocular muscles may be diagnosed based on corticosteroid responsiveness. Therapeutic management is tailored to disease severity and progress, and includes surgical debulking, corticosteroids, orbital radiation, immunosuppressive drugs, and biological agents.