Objective: Evidence suggests that perinatal factors may contribute to the development of ADHD. Our objective was to examine the association between hypertensive disorders of pregnancy (HDP) and ADHD, and behavioral difficulties among 7-year-old children. Method: The study cohort consisted of 13,192 children (weighted = 13,500) who participated in the Millennium Cohort Study (MCS) at age 7. HDP (raised blood pressure, preeclampsia, eclampsia, and toxemia) were reported by mothers 9 months postdelivery. ADHD was reported by parents at age 7 years. Weighted logistic regression models were used to assess the association. Results: In all, 1,069 (7.9%) women reported HDP and 166 (1.2%) children had an ADHD diagnosis. There was a significant association between HDP and ADHD (adjusted odds ratio [OR] = 1.78, 95% confidence interval [CI] = [1.03, 3.07]). Conclusion: These findings suggest that HDP is associated with an increased risk of ADHD. It is important to confirm this in larger cohorts and to understand the biological basis of this association.