Pathways to diagnosis in adulthood are poorly understood. Even less is known about undiagnosed adults who believe they may be autistic. This mixed-methods online survey examined adults' journeys from initial concern to receiving the diagnosis. Quantitative findings showed the diagnostic process to be highly heterogeneous. Qualitative analysis identified desires for explanation and support as motives for seeking diagnosis. Cost and fear of not being taken seriously were major barriers, echoed by qualitative responses that described the process as confusing, expensive and time-consuming. While most participants were satisfied with the diagnosis, their emotional reactions were complex. Findings support the need for thoroughly implementing national guidelines, and for improved knowledge and communication in mainstream clinicians encountering clients with possible autism characteristics.