Despite autism being defined as an exclusion criterion for selective mutism (SM) in the European diagnostic manual, many studies have revealed a significant overlap between these conditions (Keville et al., 2023; Muris & Ollendick, 2021; Sharkey & McNicholas, 2012; Suzuki et al., 2020). The purpose of this study was to examine selective mutism in Norway using data from the Norwegian Patient Register (NPR), with a specific focus on quantifying its co-occurrence with Autism Spectrum Disorder (ASD). We have identified a sample (n = 1,682), aged from 3 years to 18 years in Norway, who during the period from January 1, 2008, to April 30, 2023, have had at least one documented episode where the diagnosis of selective mutism was registered. Many individuals show a clear overlap between selective mutism and autism, at 11.7%. The Norwegian gender ratio in this SM group was 2.13 girls for every boy (M/F 1:2.13). The exclusion of autism as a co-occurring diagnosis with selective mutism in ICD-10/11 may lead to delayed or incorrect diagnoses, preventing early intervention and tailored support. This particularly affects children who experience both conditions but initially present with SM as the dominant clinical feature.
