Hallucinating psychiatric patients, patients with delusions but without a history of hallucinations and normal controls were compared on a reality-monitoring task in which they were first required to generate answers to easy or difficult clues and to listen to low-probability or high-probability paired associates. After an interval of one week, the subjects were presented with a list in which their answers to the clues were mixed with the associates and with words not previously presented, and they were required to identify the source of each item (self-generated, presented by the experimenter or new). The psychiatric patients were generally less accurate in identifying the source of the items in comparison with the normal controls. However, hallucinators more often misattributed high cognitive effort self-generated items (answers to difficult clues) to the experimenter than either the psychiatric or the normal controls. The results are interpreted as consistent with the hypothesis that hallucinations are self-generated events misattributed to an external source.