Progressive degeneration of the right temporal lobe studied with positron emission tomography. A 79 year old man with a twelve year progressive history of prosopagnosia and recent naming difficulty, in whom other intellectual skills were preserved, is described. Positron emission tomography (PET) revealed an area of right temporal lobe hypometabolism, with an additional area of less severe hypometabolism at the left temporal pole. This may represent an example of progressive focal cortical degeneration similar to that associated with primary progressive dysphasia, but affecting the right temporal lobe. 