Background: Neuropsychological deficits seems to be frequent in mental disorders. Objectives: This study reports the application of the Luria-Nebraska Neuropsychological Battery (LNNB) to four clinical groups and the results compared. Methods: Subjects were patients with first-episode schizophrenia, lucid alternating epileptic psychosis, acute alcoholic psychosis, and bipolar I. A cognitive profile was established for each group, and the profiles were compared. Results: The profiles for patients with schizophrenia, epileptic psychosis, and bipolar disorder are similar, while those with alcoholic psychosis show a different pattern of neuropsychological deficits. The specific LNNB scales with results in the abnormal range were also similar for the following pairs of groups of patients: bipolar disorder and schizophrenia; bipolar disorder and epileptic psychosis; schizophrenia and epileptic psychosis. Discussion: Neuropsychological deficit occurs frequently in various mental pathologies. In terms of functional abnormalities, the profiles of subjects with schizophrenia, epileptic psychosis, and bipolar disorder share similarities. The alcoholic psychosis group shows fewer similarities with the other three groups; the scales affected were different in comparison to the other subjects studied.