Although acute responses to traumatic stress generally resolve within a few weeks, some individuals experience severe and persistent problems, such as posttraumatic stress disorder (PTSD). While studies have identified a variety of predictors of PTSD, not all data are consistent. This longitudinal study examined the predictive power of neurocognitive deficits with regard to PTSD severity.One hundred thirty one road traffic collision (RTC) survivors were included within 2 weeks of the RTC and followed up 3 and 6 months later to determine severity of PTSD.Impairment on tests of information processing, executive functioning, verbal learning, and motor speed predicted PTSD severity when neuropsychological, clinical, and sociodemographic factors were all taken into account. Clinical variables (initial symptoms, psychiatric diagnoses, disability, trait anxiety, perceived stress, negative cognitions, and sleep) were associated with 3 and 6-month PTSD severity, but only trait anxiety was predictive of PTSD severity. Ethnicity and education were also found to be predictive.These findings suggest implementation of a holistic approach to screening for PTSD and support a need for interventions that target neurocognitive, clinical, and social variables. Early targeted profiling of this group of trauma survivors can inform early clinical interventions and policy.