Forgetfulness is defined as a subjectively bothersome impairment of the ability to recall facts that are unequivocally known to be stored in the memory. Objectifiable memory deficits may accompany numerous physical and neurological illnesses, but may also be seen in depressive states. Below average-for-age cognitive performances that do not reach the level of dementia are referred to as mild cognitive impairment, which in some cases represents a pre-dementia stage of Alzheimer's disease. Its recognition and differentiation from age-related performance deficits is now possible using simple, but sensitive neuropsychological tests. An important aim of the diagnostic work-up is the recognition of potentially reversible causes. For this purpose, physical examination and laboratory investigations are helpful. Structural and functional imaging procedures can provide information about cerebral causes. Biochemical indicators of neurogenerative processes are currently being developed. Cognitive training measures possibly have only a small and temporary effect. In patients with mild cognitive impairment, nootropic agents apparently have a symptomatic effect. Whether antidementia agents are capable of stopping the progress of mild cognitive impairment to full-blown dementia is currently being investigated in ongoing trials.