Our understanding of psychological experiences of anxiety in autism could be improved if it were shaped by autistic individuals. However, anxiety research in autism often begins with cognitive conceptualisations drawn from neurotypical or non-autistic individuals. This qualitative study aimed to explore psychological experiences of anxiety using semi-structured one-to-one interviews with a diverse sample of 20 U.K.-based, autistic adults, aged 18-55 years. Transcripts were analysed using two complementary methods: conceptual content analysis, where existing theories were tested against the data with predefined codes; and reflexive thematic analysis, where meaning was constructed from the data while considering research subjectivity. Our sample highly endorsed existing cognitive constructs: intolerance of uncertainty (100% of participants), repetitive negative thinking (100%), attentional biases (70%) and intrusive mental imagery (70%). Some autism-specific characteristics were indicated. The endorsement of imagery is particularly striking given claims that autism is often associated with weak imagery. Autistic adults described the way in which being autistic interacted with anxiety, through psychological and lived experiences. Existing support for anxiety problems was deemed insufficient and may be improved by further refining our understanding of anxiety in autism through future quantitative and qualitative research.Lay AbstractAnxiety is a top priority for research for the autistic community. We could increase our understanding of what might contribute to anxiety problems in autism by speaking to autistic people and learning about the different experiences they have had. We interviewed 20 U.K.-based autistic adults (aged 18-55 years) and asked them about their anxiety problems, including how they felt about well-known ideas of what might be involved in anxiety in autism. We looked at the answers to the interviews in two ways. The first way considers what autistic people think about the well-known ideas. The second way looks at similarities in the answers that autistic people gave. All participants' anxiety problems involved repeated negative thoughts and struggling with uncertain situations. Most also said that they tend to focus on noises or other sensory experiences within their environment and imagine situations in their mind when they are anxious. Being autistic came with challenges that could make them more anxious, including struggling with changes to routine and being bullied. Autistic people described how anxiety made their life difficult and ways in which current support for anxiety is not helpful enough. We discuss ways that we could better understand anxiety in autism and improve the support given to autistic people.