Prenatal exposure to acetaminophen may be a risk for attention-deficit/hyperactivity disorder (ADHD) in offspring, according to a new study. Data from the Norwegian Patient Registry of nearly 123,000 offspring included 2,246 patients with ADHD. Maternal use of acetaminophen during pregnancy and paternal use prior to pregnancy were evaluated. After adjusting for maternal use of acetaminophen before pregnancy, familial risk for ADHD, and indications for acetaminophen use, the researchers observed a modest association between any prenatal use of acetaminophen in one trimester (hazard ratio [HR], 1.07; 95% confidence interval [CI], 0.96-1.19), two trimesters (HR, 1.22; 95% CI, 1.07-1.38), and three trimesters (HR, 1.27; 95% CI, 0.99-1.63) and ADHD. The HR for > 29 days of maternal acetaminophen use was 2.20 (95% CI, 1.50-3.24), while use for < 8 days was associated negatively with ADHD. Acetaminophen use for fever and infections for 22 to 28 days was associated with ADHD (HR, 6.15; 95% CI, 1.71-22.05). Paternal use prior to pregnancy for ≥ 29 days was as strongly associated with ADHD as maternal use. The authors concluded that long-term maternal use of acetaminophen during pregnancy was associated substantially with ADHD, even after adjusting for indications of use, familial risk of ADHD, and other potential confounders. However, given that paternal use of acetaminophen also was associated with ADHD, the causal role of acetaminophen can be questioned. (Pediatrics 2017 Nov;140(5). pii: e20163840. doi: 10.1542/peds.2016-3840)