Approximately 50% of autistic children experience high anxiety. Intolerance of uncertainty (tendency to react negatively to uncertain situations) is a key mechanism in the development and maintenance of anxiety. This study aimed to provide a descriptive, thematic analysis of the impact on uncertainty on the daily lives of autistic children and their families. Semi-structured interviews were conducted with parents and caregivers of 53 autistic children (including 3 dyads) aged 6-16 years to elicit examples of uncertain situations that the children found challenging and to explore the impact of these situations on family life. Thematic analysis revealed five overarching themes: child's reactions to uncertainty, trying to reduce uncertainty, the impact of difficulties with uncertainty, the impact of uncertainty on parenting and the impact on parents. These findings provide a crucial understanding into the range of uncertain situations autistic children with anxiety experience. Anxiety-reduction approaches based on increasing tolerance to everyday uncertain situations could help improve well-being, quality of life and participation for autistic children and their families.