A woman presenting with levodopa responsive Parkinsonism developed rapidly progressive bulbar signs, quadriparesis, and upper and lower motor neurone signs. At necropsy, she was found to have three pathological diagnoses: amyotrophic lateral sclerosis, Parkinson's disease, and abundant tau-positive argyrophilic neuritic pathology, known as argyrophilic grain disease. This case raises the possibility that three distinct neuropathological diagnoses share a common aetiology.