ADHD, or attention-deficit/hyperactivity disorder, and autism spectrum disorder (ASD) are neurodevelopmental conditions that affect how individuals think, learn, and behave. A new study from Denmark, led by the Barcelona Institute for Global Health (ISGlobal) and Aarhus University, has found that the number of children and teenagers diagnosed with ADHD or ASD has risen significantly in recent years. However, the study also suggests that this increase may not necessarily mean there are more children with these conditions, but rather that more children are being identified and diagnosed. The research, published in the journal JAMA Psychiatry, looked at data from over 2.1 million children and adolescents in Denmark. It compared more than 71,000 young people diagnosed with ADHD or ASD between 2012 and 2022 with over 713,000 who were not diagnosed. The study found that while individuals with ADHD or ASD still had some characteristics that were previously associated with these conditions, the differences between them and the general population became smaller over time. For example, at the start of the study, children born with low birth weight were 54% more likely to be diagnosed with ADHD or ASD than those born at a normal weight. By the end of the study, this difference had decreased to 17%. Similar reductions were seen in the link between premature birth and socioeconomic disadvantage with ADHD or ASD diagnoses. This suggests that the factors previously thought to be strongly associated with these conditions are becoming less predictive over time. Researchers believe that several factors may be responsible for this shift, including greater awareness of ADHD and ASD, better identification by healthcare and education systems, and increased access to diagnostic evaluations. Changes in how neurodevelopmental traits are assessed—such as when they are considered clinically significant—may also play a role. However, the study does not quantify how much each of these factors contributed to the observed trends. The study highlights that rising diagnosis rates should not be automatically taken as proof that the actual prevalence of ADHD or ASD has increased. Instead, it shows that the group of children receiving these diagnoses has changed over time. Researchers emphasize that these findings need to be considered when interpreting current trends in diagnosis rates. They also suggest that further studies in other countries would be necessary to see if similar patterns are observed elsewhere.