Recently, there has been increasing interest in adults with pervasive developmental disorder（PDD）who seek general psychiatric services for various psychiatric problems. The diagnosis of PDD requires the careful collection of information about the patient’s developmental history. A structured diagnostic interview is useful and should be performed,but has limitations now. The clinical value of the measurement of the Wechsler Adult Intelligence Scale, the Autism-Spectrum Quotient Japanese Version, and the Pervasive Developmental Disorders Autism Society Japan Rating Scale was demonstrated by a questionnaire survey that the authors conducted in 2010. These additional tests are useful if interpreted with caution. For example,a discrepancy between the performance intelligence quotient（IQ）and the verbal IQ in the Wechsler Adult Intelligence Scale does not by itself diagnose PDD.
 We examined whether the Japanese version of the National Adult Reading Test（Japanese Adult Reading Test ; JART）, a valid scale for evaluating pre-morbid IQ in patients with schizophrenia, and the Wechsler Adult Intelligence Scale-Revised（WAIS-R）are useful for discriminating between PDD and schizophrenia. Sixteen patients with adult PDD and 16 patients with schizophrenia matched for age, education and sex participated in this study. In addition, the two groups were matched for JART and the Global Assessment of Functioning scores. All subjects were scored on the JART and WAIS-R after giving informed consent for the study. The result was that significant diagnosis-by-IQ examination interactions were found（F［1, 30］＝10.049,P＝0.003）. Also,the WAIS-R scores of the PDD group were higher than those of the schizophrenia group（P＝0.002）when the two groups were matched for JART. In conclusion, the comparison of IQ in the PDD group and in the schizophrenia group by JART and WAIS-R might be an easy and useful method for helping to discriminate between PDD and schizophrenia. In addition, the difference in IQ scores measured by JART and by WAIS-R may be helpful in diagnosing PDD.
 The diagnosis of PDD in adults may be assisted by the use of these additional tests.