In visual backward masking, a target is followed by a blank screen (ISI) and, then, a mask which deteriorates target processing. Schizophrenic patients show strong but complex processing deficits in visual masking compared to healthy controls. There is evidence for a shared genetic etiology in bipolar disorders and schizophrenia prompting the question whether both groups of patients show also analogous information processing deficits. Here, we examined whether the complex masking effects we found previously in schizophrenic patients are also found in bipolar patients. Eleven bipolar, twenty-three schizophrenic patients, and fifteen healthy controls participated in various variants of the shine-through masking paradigm. Both groups showed a very similar pattern of masking deficits. (i) Masking was strongly prolonged compared to controls: schizophrenic patients needed ISIs of 110 ms, bipolars of 95 ms, and controls of only 27 ms. (ii) These prolonged As two further experiments show, ISIs were not caused by deteriorated spatial or temporal resolution. We suggest that schizophrenic as well as bipolar patients suffer from similar dysfunctions in early visual processing. These similar dysfunctions may also have similar genetic causes.