Two cases of paranoid schizophrenia are described in which an olfactory delusion was the predominant symptom at some stage in the illnesses. A distinction is drawn between these cases, and cases of Olfactory Reference Syndrome, in which the olfactory delusion is the main feature and schizophrenic decompensation does not occur. An argument is advanced that the Olfactory Reference Syndrome (ORS) is one subtype of Monosymptomatic Hypochondriacal Psychosis (MHP) and reference is made to evidence suggesting that pimozide may be a specific and effective treatment in the various presentations of MHP.