It is recognised that a high proportion of adults on the autism spectrum experience depressive symptoms. However, limited research has explored autistic peoples' experiences of low mood and depression. The aim of this study was to explore the lived experiences of low mood and depression for adults on the autism spectrum. The study employed Interpretive Phenomenological Analysis to investigate the experiences of 8 adults (7 males and 1 female), aged between 19 and 51, who had a diagnosis of autism without co-occurring learning disabilities, and experienced low mood or depression. All participants recorded their thoughts and feelings in a mood diary for 1 week and participated in a semi-structured interview. Three superordinate themes emerged from the data: 'Autism has made me the person I am', 'I can't function in the world' and 'It's like trying to do accounts on the futures market': Making sense of emotions. Findings highlight a need for specialist mental health provision for adults who are on the autism spectrum. Limitations of this study and implications for future research are discussed.