Background: Altered brain development is common after preterm birth, and reduced brain volume in childhood has been associated with functional impairments. However, limited information is available about perinatal factors that may be related to brain volumes in mid-childhood. We examined the association between size at birth and brain volumes at nine years of age. Methods: Children born at 36 to 42 weeks’ gestation at risk of neonatal hypoglycaemia underwent brain magnetic resonance imaging (MRI) at nine years of age. Volumes of total brain, total cortical grey matter and cerebral white matter, subcortical grey matter, and regional structures (frontal, parietal, occipital, and temporal lobes, cerebellum, cerebrospinal fluid) were analysed using the FreeSurfer tool. Relationships between brain volumes and gestational age at birth, birth weight, and head circumference were analysed using linear regression. Results: In the 101 children (49 boys), shorter gestation at birth (R2=0.10, p= <0.001), lower birth weight (R2=0.13, p= <0.001), and smaller head circumference (R2=0.17, p= <0.001) were associated with smaller total brain volume at nine years of age. The associations with birth weight and head circumference remained significant after accounting for gestational age at birth. There was also a positive association between these perinatal factors and most other brain volumes we studied, but not with cerebellum, occipital lobe, and cerebrospinal fluid volumes. Conclusion: Size at birth is associated with brain volumes at nine years of age, suggesting that both growth before and timing of birth might be important for later brain size.