Research suggests that individuals with psychiatric illness may be at an increased risk for traumatic brain injury (TBI) (Fann et al., 2002). Those who sustain mild TBI are at risk of persistent psychiatric disorder (Fann et al., 2004). Preinjury psychiatric illness has also been proposed as a predictor of persistent postconcussion syndrome (PCS) following mild TBI (Carroll et al., 2004). Few studies, however, have investigated the relationship between preinjury psychiatric illness and the aetiology of PCS. The aim of the current study was to examine predictors of acute PCS (within the first 14 days after injury) in a prospective sample of consecutive trauma admissions to a Level 1, trauma hospital. The final sample comprised 90 mTBI and 85 non-brain injured trauma controls. Preinjury psychiatric disorder, demographic factors, injury-related characteristics, neuropsychological and psychological variables were examined as predictors of acute PCS. Multiple imputation of missing data in multivariable logistic regression was used to predict acute PCS, a mean 4.90 days postinjury. The strongest effect for acute PCS was at least one previous affective or anxiety disorder. Female gender was the next largest effect. Higher IQ, response speed, acute posttraumatic stress and pain were also significant predictors of acute PCS.