Objective  To assess long term outcomes of children from pregnancies complicated by twin-to-twin transfusion syndrome.

Design  Comparison of children from pregnancies with twin-to-twin transfusion syndrome in Western Australia with a contemporaneous regional comparison cohort of preterm and term infants studied using an identical assessment procedure.

Population and setting  All infants aged ≥18 months were identified from a geographically based longitudinal cohort of monochorionic twin pregnancies with an antenatal diagnosis of twin-to-twin transfusion syndrome conducted prospectively since 1992.

Methods  Children were evaluated using age-specific developmental and behavioural assessments. Cerebral palsy was diagnosed clinically and ascertainment confirmed through the Western Australian Cerebral Palsy Register.

Main outcome measures  Intellectual disability, cerebral palsy, behavioural and cognitive function.

Results  Fifty-two children were identified as eligible for study and assessments were performed on 49 (94%). Three surviving children had a diagnosis of cerebral palsy (5.8%). The mean IQ score was 8 points lower in twin-to-twin transfusion syndrome children compared with the comparison cohort although this was mainly due to a decrement of 13 points in those born before 33 weeks of gestation. There was no difference between the donor and the recipient twin in terms of IQ scores (median difference −3, 95% CI −9 to 6). There was no relationship of IQ score to the worst stage of the twin-to-twin transfusion syndrome. Child Behavior Check List and Vineland Adaptive Behavior Scale scores did not differ between twin-to-twin transfusion syndrome children and the comparison group.

Conclusions  Twin-to-twin transfusion syndrome is associated with a significant reduction in IQ score in very preterm survivors. There seems to be no increase in the prevalence of cerebral palsy. Overall behaviour and adaptive behaviour scale scores are similar to a comparison group.