Objective: Factor analytic research has been inconsistent regarding the latent structures underlying neuropsychological batteries in psychotic disorders. Furthermore, despite evidence of familial patterns of neurocognitive dysfunction no studies have examined the cognitive architecture underlying neuropsychological batteries among first-degree relatives of psychotic patients. Method: The present study examined the latent factor structure of the Brief Assessment of Cognition in Schizophrenia (BACS) using complimentary, empirically driven, and theoretically guided techniques. Separate analyses were conducted on 1000 psychosis spectrum probands (schizophrenia, schizoaffective, psychotic bipolar), 1000 of their first-degree relatives, and 400 non-psychiatric controls from the Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) consortium. Results: Exploratory factor analysis clearly indicated a single-factor solution for all groups and confirmatory factor analysis indicated a better overall fit than a three-factor model. Conclusion: The BACS assesses a similar cognitive construct in probands, relatives, and controls, which appears to be a generalized cognitive factor. Neuropsychological assessment of this generalized dysfunction with brief batteries offers high efficiency, and has been reliably linked to functional outcome.