This study is the first to examine a large group of children born after in-vitro fertilization (IVF) who were old enough at the time of the investigation to make it possible to draw conclusions about the outcome. The aim of the study was to assess the cognitive, behavioural and social development of the children. The study comprised 99 IVF children, 33-85 months of age, from the University Hospitals of Lund and Malmö, Sweden. The children's development was assessed with the Griffiths' scales of mental development. The children's behaviour was delineated through semi-structured interviews with their mothers, covering 50 different behaviours. The mothers also filled in Achenbach's Child Behaviour Checklist (CBCL). All children were examined by a paediatric neurologist. The results were compared to Swedish population groups. Of the children born, 66% were singletons, 22% were twins, 12% were triplets and 28% were born prematurely in gestational weeks 32-36. The cognitive development of the IVF children was excellent, and their behaviour was normal when compared with two Swedish population groups. Our conclusion was that the development, behaviour and social adaptation of the children was very satisfactory.