Objectives: To determine the degree of agreement of the OPCRIT diagnostic systems in the diagnosis of Schizophrenia. Method: A total of 112 case notes (67.9% men and 32.1% women), of Bahraini Schizophrenic patients with ICD-10 classification formed the Schizophrenic population for this study. These 112 patients who were analyzed attended the out-patient department at the Psychiatric Hospital in Bahrain until the year 2008. The OPCRIT 3.31 checklist was applied as a diagnostic tool. The kappa coefficient and percentage of agreement were used to measure the concordance and absolute agreement of the OPCRIT diagnostic systems of Schizophrenia. Results: The diagnoses of Schizophrenia using ICD 10, DSMIII-R. Research Diagnostic Criteria (RDC) and Tsung and Winokur (TS and WI) all have strong and excellent agreement with each other. The strongest is between RDC and TS &WI (Kappa 0.936). The diagnosis of Schneider (SCHN), French (FREN), CROW and Farmer (FARM) all have low kappa values of agreement (less than 0.4) with other diagnoses except FREN with DSMIII-R (0.451). The absolute percentages were high for all diagnostic systems except for the diagnosis of CROW. Conclusion: The diagnostic systems of ICD-10, DSMIII-R, RDC, and TS and W1 have strong diagnostic agreements (kappa < 0.780). The strongest is between RDC and TS&W1 (kappa 0.936), while Schneider French, Crow, and Farmer have low diagnostic agreements (Kappa>0.4) However, French and DSM/III-R maintained higher diagnostic agreement (Kappa 0.451). Results direct the need for a cautious level of confidence and validity of officially designated classification systems.