Visual backward masking is a very sensitive tool for studying early visual processing deficits and a reliable endophenotype of schizophrenia. Mental diseases strongly overlap in many aspects, for example, in psychopathology, cognition, and genetics. Here, we show that strong masking deficits are found in patients with functional psychoses but not in non-psychotic patients, namely, depressive patients and abstinent alcoholics. We tested 28 schizophrenic, 22 schizoaffective, 20 bipolar patients, 26 major depressive patients, 23 abstinent alcoholics, and 24 healthy control subjects with various variants of the shine-through masking paradigm. Patients with schizophrenia, schizoaffective disorder, and bipolar disorder, show strongly prolonged SOAs compared to controls. Patients with unipolar major depression and abstinent alcoholics, however, perform like healthy controls. We suggest that patients with functional psychoses suffer from similar visual dysfunctions whereas visual processing of depressive patients seems to differ. [The work was supported by the Volkswagen Foundation.]