Daytime activity, in terms of engagement in an occupation or education, is highly important for individuals with autism spectrum disorder (ASD), regardless of their level of functioning. In this nationwide survey, the parents of young adults diagnosed with ASD in childhood (n = 1266) provided information about the current daytime activity of their child, as well as behavioral characteristics, comorbidity, history of schooling during primary and secondary school, and availability of support. The young adults without a regular daytime activity constituted approximately one-fifth of the sample and had more behavioral difficulties and comorbidities than young adults with a daytime activity. Intellectual disability, part-time job, history of schooling, including type of school, and availability of support were found to be associated with daytime activity.