Attentional dysfunction is considered as one of the core deficits in schizophrenic process. The findings, pathophysiological mechanisms, and their clinical implications of clinical and experimental neurocognitive tests for the attentional impairment in schizophrenics are reviewed. The influences of psychopathology, antipsychotic treatment, and chronic institutionalization are also included in the review. In contrast, there are only a few evidences that attentional dysfunction would be a core deficit of depressive, manic, and anxiety disorders. Some recent findings of attentional impairment in these disorders are reviewed.