Dementia is a common problem in elderly patients and may influence the indication for invasive diagnostic and therapeutic procedures under consideration for other diseases more than age itself. This short paper reviews the role of tomographic imaging techniques--whose possibilities have expanded in recent years--in the differential diagnosis of dementia. Computerized tomography (CT) of the brain is used primarily to detect such potentially treatable conditions as multiple ischemic infarctions, hematomas, hydrocephalus and brain tumors. It should be performed even in old age, unless the patient's general state of health is too poor to expect good results from therapeutic measures. Magnetic resonance imaging is more sensitive in ischemic white matter lesions and hippocampal atrophy, and should therefore be used preferentially in mildly affected patients. Functional imaging methods, such as SPECT and PET, are needed only to demonstrate impairment of cortical blood flow and metabolism in clinically unclear cases.