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Background: The fourth edition of Diagnostic and Statistical Manual of Mental Disorders (DSM IV) distinguishes schizophrenia, schizophreniform disorder and brief psychotic disorder only according to the duration of the illness. Thus, the validity of these nosological concepts sounds uncertain., Aim: The aim of this study was to evaluate the validity of the DSM IV concepts schizophrenia, schizophreniform disorder and brief psychotic disorder., Population and Methods: Seventy schizophrenics, 68 patients with brief psychotic disorder and 50 with schizophreniform disorder, all Congolese people, selected from the 'Telema' Mental Health Centre and the 'Neuropsychopathological centre of the University of Kinshasa, from 5(th) August 2003 to 14(th) March 2005 were compared with respect to the following clinical parameters: family schizophrenia and brief psychoses history, precipitating psychosocial factors, mode of onset of the disease, clinical syndromes linked to psychoses and general functioning. Statistical analyses included analysis of variances 'one way' (Anova), post hoc Tukey's test, discriminant analysis, and analysis of covariances., Results: Brief psychotic disorder differed from schizophrenia and schizophreniform Disorder in respect with positive syndrome (F=8.76, df=2; 179, p=0.0002), cognitive syndrome (F=3.79, df=2; 179, P=0.024), syndrome of excitement (F=3.23, df=2; 179, P=0.042), general functioning (F=13.73, df=2; 179, P<0.0001), family history of schizophrenia (χ(2)=8.65; P=0.013), precipitating psychosocial factors (χ(2)=19.82; P<0.0001), and mode of onset of the disease (χ(2)=91.3; P<0.0001). Schizophreniform disorder differered from schizophrenia only by a more frequent acute onset and a better general functioning. Two nosological realities were thus distinguishable: brief psychotic disorder and schizophrenia-schizophreniform disorder complex. Surprisingly, negative syndrome could not distinguish brief psychotic disorder from schizophrenia and schizophreniform (F=2.80, df=2; 179, P=0.063). Data of the discriminant analysis based on scores on general functioning, positive, negative, depressive, cognitive and excitement syndromes was conclusive (F=6.41, df=2; 185, P<0.0001) and allowed correct classification rates of 75% for brief psychotic disorder, 48% for schizophreniform disorder, 54% for schizophrenia. Schizophreniform disorder was thus the less distinguishable group; this is in the line with longitudinal studies, which demonstrated the lowest diagnostic stability of this affection, compared with the two other diseases. Total error rate was 41%., Conclusions: Brief psychotic disorder could constitute a distinct affection from schizophrenia and schizophreniform disorder, whereas schizophreniform disorder and schizophrenia could be the same affection; the first being an acute and "good functioning" form of the second. However, these viewpoints need to be confirmed by data on long-term course. The data of this study validate ultimately a binary model of the major nonaffective functional psychoses, like that of the tenth edition of the International classification of mental and behavioural disorders (ICD-10)., (Copyright © 2010 L'Encéphale, Paris. Published by Elsevier Masson SAS. All rights reserved.)