Internet-based questionnaires (e-questionnaires) have become widely used in psychopathology research, but there is currently little evidence on their reliability as compared with pen-and-paper equivalents. Data from separate samples of young adults completing e-questionnaires on hallucination-proneness (N = 751) and persecutory ideation (N = 183) were compared with data from pen-and-paper versions of the same questionnaires completed by a third, unrelated sample (N = 188). There was no effect of modality of presentation on mean scores on these questionnaires. Multi-group confirmatory factor analysis indicated mode invariance of factor structure for the persecutory ideation questionnaire. Internal reliability of both questionnaire formats was satisfactory. We conclude that the administration of traditional measures of psychopathology via e-questionnaire is a reliable method of data collection.