Prevalence of ASD, ADHD and co-occurring conditions among children and adolescents in the Faroe Islands, 2004-2022: a nationwide register-based study

Abstract Objective To investigate the prevalence of autism spectrum disorders (ASD), attention deficit/hyperactivity disorder (ADHD), and related co-occurring conditions in Faroese children and examine differences regarding sex and age at diagnosis. It is hypothesised that prevalences are increasing, are higher in boys compared to girls, that girls are diagnosed later than boys, and that stress-related mental health conditions are related to higher age at diagnosis. Methods A retrospective study was conducted with children born from 2004 to 2022, using health register data on patients diagnosed with ASD or ADHD at the National Hospital of the Faroe Islands. A total of 479 children were included in the study. Prevalence rates were calculated alongside age- and sex-standardised measures, including the mean age at diagnosis and the frequency of co-occurring conditions, with all estimates including 95% confidence intervals (CI). Results Prevalence of ASD was 2.7% (95% CI: 2.4–3.0), with a higher prevalence among boys (3.4%, 95% CI: 2.9–3.9) compared to girls (2.0%, 95% CI: 1.6–2.4). Prevalence of ADHD was 2.9% (95% CI: 2.6–3.3), higher in boys (3.8%, 95% CI: 3.3–4.4) than in girls (2.0%, 95% CI: 1.6–2.4). Girls received diagnoses of ASD and ADHD at later ages—on average, 12.7 years for ASD, 11.9 years for ADHD, compared to 9.5 and 10.8 years, respectively, for boys. The mean ages at diagnosis were 14.2 years for ASD and 12.3 years for ADHD for those children who also presented with stress-related mental health conditions. Children without these conditions were diagnosed at mean ages of 9.4 and 10.3 years, respectively. Conclusion Childhood ASD and ADHD prevalence in the Faroe Islands was 2.7% and 2.9%, with sex distributions consistent with international patterns and frequent co-occurring conditions. Differences in diagnostic age linked to stress-related mental health conditions were observed, though these findings require cautious interpretation. Earlier identification may facilitate timelier intervention and reduce subsequent mental health risks.