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This study examined the effects of traumatic brain injury (TBI) on Wechsler Memory Scale-III (WMS-III) performance. Since poor effort potentially contaminates results, effort was explicitly assessed and controlled using two well-validated cognitive validity indicators, the Portland Digit Recognition Test (PDRT) and Reliable Digit Span (RDS). Participants were 44 mild TBI patients with good effort, 48 mild TBI patients with poor effort, and 40 moderate–severe TBI patients with good effort. A dose–response relationship between injury severity and WMS-III performance was demonstrated. Effect size calculations showed that the good effort mild TBI patients did not differ from normal (average Cohen's d= 0.07) while moderate–severe TBI had a moderate effect on WMS-III scores (average Cohen's d=−0.52). Consistent with previous literature, the moderate–severe TBI group scored the lowest on WMS-III Visual indices. Effort had a larger effect than injury severity on WMS-III scores (average Cohen's d=−1.27). Clinical implications of these findings are discussed.