['In preterm infants, white matter (WM) abnormalities detected on magnetic resonance imaging (MRI) at term-age are associated with early developmental delay. We set out to study this association in adolescents born pre-term, by examining intellectual outcome in relation to markers of brain injury, focusing on the effects of WM reduction.', "Seventy-nine participants were recruited and assessed at a mean age of 16 years: 49 adolescents born preterm (<32 weeks' gestation) with a wide spectrum of brain injuries (including 22 with no identifiable brain injury at birth) and 30 term-born controls. Data collected included: brain MRI scans, full-scale intelligence quotient (IQ) scores, educational attainments, and behavioral scores. Measures of WM reduction included total volume, cross-sectional area of the corpus callosum (CC), and ventricular dilatation. Cerebellar volumes and neuroradiological ratings were also included.", 'WM volume and IQ were reduced in the preterm groups (both with and without brain injury). Total WM volume and CC area jointly explained 70% of IQ variance in the adolescents born preterm, irrespective of the presence or severity of brain abnormalities detected at birth or on follow-up MRI. This relationship was not seen in controls. Importantly, correlations were also found with real-world measures of academic achievement and behavioral difficulties.'] Is total brain white matter a major determinant of IQ in adolescents born preterm?