Context: Worldwide, millions of patients with traumatic brain injury (TBI) suffer from persistent and disabling intelligence impairment. Post-traumatic amnesia (PTA) duration is a promising predictor of intelligence following TBI. Objectives: To determine (1) the impact of TBI on intelligence throughout the lifespan and (2) the predictive value of PTA duration for intelligence impairment, using meta-analytic methods. Methods: Electronic databases were searched for peer reviewed articles, published until February 2012. Studies reporting intelligence following TBI and injury severity by PTA duration were included. Meta-analytic methods generated effect sizes for full scale IQ (FSIQ), performance IQ (PIQ) and verbal IQ (VIQ), following mild TBI (PTA duration 1-24 h) and severe TBI (PTA duration >7 days), during the subacute phase of recovery (≤6 months post-injury) and the chronic phase (>6 months post-injury). Meta-regression elucidated the predictive value of PTA duration for intelligence impairment. Results: Patients with severe TBI exhibited large depressions in FSIQ in the subacute phase of recovery (d=-1.07, 95% CI to 1.52 to -0.62; p<0.001), persisting into the chronic phase (d=-0.78, 95% CI -1.06 to -0.51; p< 0.001). PIQ was more severely affected than VIQ in the subacute phase (Q(1) =3.85; p<0.05) but not in the chronic phase (Q(1) =0.03, p=0.87). Most importantly, longer PTA duration strongly predicted greater depressions of FSIQ and PIQ in the subacute phase (-0.76 ≤ βs ≤ -0.73, Ps<0.01) and FSIQ, PIQ and VIQ in the chronic phase (-0.80 ≤ βs ≤ -0.61, Ps<0.05). Conclusions: PTA duration is a valuable predictor of intelligence impairment following TBI. Results support the routine assessment of PTA duration in clinical settings.