Cerebral toxoplasmosis can lead to dementia in AIDS and in immunodeficient patients. We present a case study in which cerebral toxoplasmosis was associated with a dementia of Alzheimer type. Half a year to one year before the cognitive impairment began, the patient suffered a subacute infection of toxoplasmosis at the age of 56. Neuropsychological examination as well as MRI suggested a diagnosis of dementia with infectious genesis. However, serological tests showed only little evidence of infection. Since the results of the PET examination indicated changes in the glucose metabolism typical of Alzheimer's disease,we infer a comorbidity of cerebral toxoplasmosis and dementia of Alzheimer type.