In this long-term follow-up of children following very preterm (VP) birth, we applied fixel-based analysis to study white matter development. At ages 7 and 13 years, VP children had reduced fibre density and cross-section throughout the white matter compared with full-term controls. Longitudinally, VP children had slower macrostructural development of commissural and motor pathways between ages 7 and 13 years. Younger gestational age, smaller birth weight and neonatal brain abnormalities were associated with lower fibre density and cross-section at both ages. Thus, VP birth and concomitant perinatal risk factors are associated with long-term delays and/or disruptions to white matter development.