The factorial structure of negative symptoms in medication naïve First Episode Psychosis sample Demjaha A, Galderisi S, Arango C, Rodriguez-Jimenez R, Mucci A, Bobes J, Garcia-Portlla P, Dazzan P, McGuire P Institute of Psychiatry, Psychology and Neuroscience, King’s College London United Kingdom RESULTS The CFA indicated a good fit for two-factor model of negative symptoms: CFI = 0.98 GFI = 0.97 TLI = 0.97 RMSEA = 0.06 (CI 90%: 0.04–0.08) Two factor model of negative symptoms in Optimise FEP sample with correlated residuals indicated by red lines. CONCLUSION Our results demonstrate that the two-factor structure is supported even in medication naïve patients with first episode psychosis. Dimensional approach may improve the understanding of pathophysiology and lead to identification of novel therapeutic targets for negative symptoms.  Future research should focus on differential pathophysiology and clinical correlates of these domains. REFERRENCES Liemburg E, Castelein S, Stewart R, van der Gaag M, Aleman A, Knegtering H. Two subdomains of negative symptoms in psychotic disorders: established and confirmed in two large cohorts. J Psychiatr Res. 2013; 47: 718–25. Blanchard JJ, Cohen AS. The structure of negative symptoms within schizophrenia: implications for assessment. Schizophr Bull. 2006; 32: 238–45 Kirkpatrick B, Fischer B a. Subdomains within the negative symptoms of schizophrenia: commentary. Schizophr Bull. 2006; 32: 246–9 Strauss GP, Horan W, Kirkpatrick B, Fischer B a, Keller WR, Miski P, et al. Deconstructing negative symptoms of schizophrenia: avolition-apathy and diminished expression clusters predict clinical pre- sentation and functional outcome. J Psychiatr Res. 2013; 47: 783–90   INTRODUCTION Negative symptoms of Schizophrenia are typically considered as a single dimension. However, factor analytic studies consistently report two domains of negative symptoms: Expressive Deficits (ED) and Social-Amotivation (SA). 1-4 Research to date has focused on chronic and medicated samples. We examined whether this two-factor model of negative symptoms can be confirmed in medication naïve first episode psychosis (FEP) STUDY DESIGN The sample comprised 469 FEP medication-naïve patients recruited through Optimise Trial (http://www.optimisetrial.eu). Negative symptoms ratings were obtained prior to starting medication by using the Positive and Negative Syndrome Scale (PANSS). Data-driven selection of items that reflect negative symptoms in the PANSS was used.1 Based on published research the following symptoms were included: Flat Affect (N1) Emotional Withdrawal (N2) Poor Rapport (N3) Passive Social Withdrawal (N4) Lack of Spontaneity (N6) Mannerisms and Posturing (G5) Motor Retardation (G7) Avolition (G13) Active Social Avoidance (G16) Confirmatory Factor Analysis (CFA) Using computer programme AMOS, CFA was performed to examine identified two factor model. The previously identified factors SA (N2, N4, G16) and ED (N1, N3, N6, G5, G7, G13) were entered as latent variables. Multiple indices were used to measure the goodness-of-fit (GOF): Comparative Fit Index (CFI) Goodness of-Fit index (GFI) Tucker-Lewis index (TLI) Root-Mean-Square-Error-of-Approximation (RMSEA) ACKNOWLEDGEMENTS OPTIMISE Consortium