The Eppendorf Schizophrenia Inventory (ESI) is a new clinical questionnaire aimed at self-experienced cognitive disturbances that are considered to be diagnostically specific for schizophrenia. Two ESI validation studies are presented in this report. The aim of study I was to search for objective correlates of the ESI in 100 schizophrenic inpatients. In study II, the diagnostic validity of the ESI was examined by group comparisons (inpatients with first episode or chronic schizophrenia, alcoholism, depression, or obsessive-compulsive disorder, and healthy adults). Study I yielded numerous plausible correlations between ESI subscales and other clinical scales, neuropsychological tests, psychopathological interview data, and neurological symptoms. Study II supported the diagnostic validity of the ESI. A confirmatory factor analysis conducted with the combined schizophrenic sample from both studies corroborated the assumed factor structure. These results confirm the reliability and validity of the ESI.