Heterogeneity in progressive aphasia due to focal cortical atrophy. A clinical and PET study. Six patients with a slowly progressive aphasic disorder due to degenerative cortical disease are reported. The length of history varied from 18 months to 6 years. In 5 patients, there was a naming deficit, associated in 4 of these with some abnormalities in comprehension. One patient had a progressive history of reduced speech output, which was associated with an orofacial dyspraxia. All patients were studied neuropsychologically, and in addition regional cerebral metabolism was measured using position emission tomography. A localized left hemisphere deficit was found in all patients except 1, who had the longest history and the most profound clinical deficit, and who also had right hemisphere hypometabolism. The major brunt of the deficit was in the anterior portion of the left temporal lobe in all but 1 case, the patient with poor speech output who had a more severe left posterior frontal deficit. These findings suggest that in progressive aphasia due to focal cortical atrophy there is heterogeneity in the clinical presentation and anatomical site of the deficit, with possible implications for the underlying aetiology. 