OBJECTIVE: To compare neurodevelopmental outcomes of extremely preterm infants conceived after assisted conception (AC) compared with infants conceived spontaneously (non-AC). DESIGN: Population-based retrospective cohort study. SETTING: Geographically defined area in New South Wales and the Australian Capital Territory, Australia served by a network of 10 neonatal intensive care units. PATIENTS: Infants <29 weeks' gestation born between 1998 and 2004. INTERVENTION: At 2-3 years corrected age, 1473 children were assessed with either the Griffiths Mental Developmental Scales or the Bayley Scales of Infant Development. MAIN OUTCOME MEASURE: Moderate/severe functional disability defined as developmental delay (Griffiths General Quotient or Bayley Mental Developmental Index >2 SD below the mean), cerebral palsy (unable to walk without aids), deafness (bilateral hearing aids or cochlear implant) or blindness (visual acuity <6/60 in the better eye). RESULTS: Mortality and age at follow-up were comparable between the AC and non-AC groups. Developmental outcome was evaluated in 217 (86.5%) AC and 1256 (71.7%) non-AC infants. Using multivariate adjusted analysis, infants born after in-vitro fertilisation at 22-26 weeks' gestation (adjusted OR 1.79, 95% CI 1.05 to 3.05, p=0.03) but not at 27-28 weeks' gestation (adjusted OR 0.81, 95% CI 0.37 to 1.77; p=0.59) had higher rate of functional disability than those born after spontaneous conception. CONCLUSIONS: AC is associated with adverse neurodevelopmental outcome among high risk infants born at 22-26 weeks' gestation. This finding warrants additional exploration.