Agreement of diagnosis of psychiatric disorders by psychologists was examined in case vignette and inter-rater designs. In the case vignette design, the agreement of 3 graduate psychology students for the Research Diagnostic Criteria (RDC) diagnosis was high for the most of the RDC diagnostic categories, except for Schizotypal Features. In the inter-rater design, disagreement was only observed among 2 out of 11 psychiatric in-patients. This suggested that an operationalized criteria could enable psychologists to establish diagnosis of psychiatric disorders reliably and therefore communicate and collaborate with psychiatric researchers.