A case is reported of the rare association between progressive multifocal leucoencephalopathy and carcinoma. A 66-year-old man underwent a laryngectomy for carcinoma. Four years later he developed a local recurrence. Simultaneously there were behavioural disturbances and a left motor neglect followed by dense hemiplegia and coma. The patient died a further 5 months later. Anergy was demonstrated by skin tests. CT scan showed asymmetrical non-enhancing low-density areas in the hemispheric white matter, brain-stem and cerebellum and neuropathological examination confirmed extensive myelin loss with typical papovavirus inclusions in oligodendrocytes identified by electron microscopy.