OBJECTIVE: To assess the association of fertility treatment and subfertility with offspring intelligence, attention, and executive functions in 5-year-old singletons. DESIGN: Follow-up study. SETTING: Denmark 2003-2008. POPULATION: A cohort of 1782 children sampled from the Danish National Birth Cohort. METHODS: The children were tested with a neuropsychological battery at age five. In addition to tests of intelligence, attention and executive functions, the follow up included extensive information on important covariates. The analyses were conducted using multiple linear regression and adjusted for parental educational level, maternal intelligence, age, parity, body mass index, smoking in pregnancy, alcohol consumption in pregnancy and child gender, child age, and examiner. MAIN OUTCOME MEASURES: Wechsler Preschool and Primary Scale of Intelligence-Revised, the Test of Everyday Attention for Children at Five, and the Behavior Rating Inventory of Executive Functions scores. RESULTS: A consistent pattern of nonsignificantly lower scores were only observed for intelligence and executive functions in children born after fertility treatment or by subfertile parents when the results were unadjusted for maternal intelligence and parental educational level. When adjusted for these and other covariates, there were no significant mean differences in intelligence (mean difference -2.8, 95% CI -7.8, 2.2), overall attention (-0.1, 95% CI -0.6, 0.3), or parent-rated executive functions (-0.1, 95% CI -3.0, 2.9) between children born after spontaneous conception and children born to parents conceiving after fertility treatment. Similarly, there were no significant mean differences in intelligence (mean difference 0.6, 95% CI -2.2, 3.4), overall attention (0.1, 95% CI -0.2, 0.4), or parent-rated executive functions (1.0, 95% CI -1.8, 3.7) between children born after spontaneous conception and children born to subfertile parents waiting more than 12 months before conceiving naturally. CONCLUSIONS: This study suggests that parental subfertility and fertility treatment are unrelated to offspring intelligence, attention and executive functions.