The psychopathology of acute organic psychosis was investigated by interviewing 74 patients using the Present State Examination (PSE). Their delusions, perceptual disturbance, thought disorder, and emotional disorder were categorised and then compared with those seen in 74 acute schizophrenics. In acute organic psychosis there was a particular pattern to the delusions, perceptual disturbance, and thought disorder, which was quite unlike that seen in acute schizophrenia. These results have implications for theories claiming that schizophrenia is an organic psychosis. It is suggested that the psychopathology in acute organic psychosis has very different origins from that seen in schizophrenia.