Summary : The aim of this work is to find out and assess the different cognitive deficits in patients wit Alzheimer's disease and schizophrenia patients to help in early detection and management. The review included Introduction. Chapter 1: Cognitive processes. Chapter 2: Cognitive deficits in schizophrenia. Chapter 3: Cognitive deficits in AD. Chapter 4: Cognitive assessment. Chapter 5: Management. The practical part included Subjects and methods: The sample was divided into two groups: first group for patients with Alzheimer's disease (n=20), second group for patients with schizophrenia (n=20), according to the DSM-IV criteria. These patients were subjected to the following tools: CAMCOG test: a neurocognitive battery that comprises the cognitive examination part of a standardized psychiatric assessment schedule, CAMDEX (The Cambridge examination for mental disorders of the elderly). The 19 items used in the Mini Mental State Examination of Folstien (MMSE) are incorporated in the CAMCOG test, however, a number of additional items have been added to make the cognitive section more comprehensive. Several functions are assessed in greater detail than in a number of widely used schedules. For example, memory is assessed in the MMSE only by the repition and recall of three words; while the CAMCOG have added items covering remote and recent memory and the recall and recognition of new information. Thus the cognitive section of the CAMDEX (the CAMCOG) provides wide coverage of cognitive functions as well as a large body of information about most functions. Wisconsin Card Sorting Test (WCST): this test was used to assess abstract reasoning ability, the ability to shift cognitive strategies in response to changing environmental contingencies, strategic planning and organized searching. the WCST can be considered a measure of "executive function. Because of its apparent sensitivity to the effects of frontal lobe lesions, the WCST is often referred to as a measure of "frontal" or "prefrontal" functioning. WAIS test: provides in addition to the IQ and deterioration index, the subtests of WAIS assess several cognitive functions both verbal and performance. MRI: was used in our work as a structural neuroimaging of the brain, helping to identify a number of brain abnormalities in schizophrenia as well in Alzheimer's disease.