Data are from the Norwegian Medical Birth Registry and linked population registers from January 1, 1991, to December 31, 2009. Adjusted odds ratios (ORs) represent ORs after adjustment for sex, year of birth, mother’s age, parity, maternal marital status, maternal and paternal educational attainment, and parental immigrant status. Error bars indicate 95% CIs. ADHD indicates attention-deficit/hyperactivity disorder; ASD, autism spectrum disorder.