Introduction: Currently, almost three percent of children are born with the help of assisted reproductive technologies (ART) such as in vitro fertilisation (IVF) or intra cytoplasmic sperm injection (ICSI). This raises the important question whether ART influences developmental outcome. The aim of this study was to evaluate cognitive and behavioural outcome at 9 years in children conceived with ART. Patients and Methods: The Groningen ART cohort study has a prospective design. The cohort consists of children born following IVF or ICSI with conventional controlled ovarian hyperstimulation (COH-IVF/ICSI), children born following IVF/ICSI in the modified natural cycle (MNC-IVF/ICSI) and children born after natural conception to subfertile couples (Sub-NC group). At 9 years 57 COH-IVF, 46 MNC-IVF, and 66 Sub-NC singleton children were assessed. Cognition was assessed with the Wechsler Abbreviated Scale of Intelligence (WASI), behaviour was assessed with the Child Behaviour Checklist (CBCL) and Teacher Report Form (TRF). Univariable analyses and multiple linear regression models were used. Results: There was no significant difference in IQ scores between ART groups (p=0.746). Multivariable analyses did not show influence of ART group on total, verbal and performance IQ. CBCL and TRF scores did not differ significantly between ART groups (p=0.090 and p=0.507). Multivariable analyses did not show influence of ART group on CBCL and TRF total, internalizing and externalizing T-scores. Conclusion: ART did not influence cognitive and behavioural outcome at 9 years. These are reassuring results for both parents and clinicians involved in ART.