Aim: The Infant Motor Profile (IMP) is a qualitative assessment of motor behaviour of infants aged 3 to 18 months. The aim of this study was to investigate construct validity of the IMP through the relation of IMP scores with prenatal, perinatal, and neonatal variables, including the presence of brain pathology indicated by neonatal ultrasound imaging of the brain. Method: A longitudinal prospective study was performed in a group of 30 term infants (12 females, 18 males; median gestational age 40.1wks, range 37.6-42wks) and 59 preterm infants (25 females, 34 males; median gestational age 29.7wks, range 25-34.7wks). IMP assessments were performed at (corrected) ages of 4, 6, 10, 12, and 18 months. Socio-economic and perinatal data were collected, which, in the case of preterm infants, included information on periventricular leukomalacia and intraventricular hemorrhage based on neonatal cranial ultrasound. Data were analysed by fitting mixed-effects models. Results: Gestational age, socio-economic status, and 5-minute Apgar scores were significant determinants of IMP scores in the total group of infants (p less than 0.001, less than 0.002, and less than 0.042 respectively). In the subgroup of preterm infants, IMP scores were significantly affected by brain lesions on neonatal ultrasound (p less than 0.001) and by socio-economic status (p = 0.001). Interpretation: The findings support the construct validity of the IMP: IMP scores are clearly associated with relevant determinants of neuromotor function.