Background: An emerging literature suggests that autistic adults are at increased risk of experiencing suicidal thoughts, making suicidal plans and attempts, and dying by suicide. However, few studies have investigated whether autistic traits are related to suicidal behaviour. The current study examined autistic traits in a sample of adults who reported at least one suicide attempt. Methods: An online questionnaire was advertised between June and September 2017 on suicide prevention websites, research databases, and social media. Participants reported whether they had ever attempted suicide (yes/no), and if so, how many times they had attempted (once/more than once). They also reported diagnosed and suspected mental health or neurodevelopmental conditions, and completed the Autism Spectrum Quotient (AQ). Two hundred forty-five adults accessed the survey; 132 reported having attempted suicide and also completed the AQ. It was hypothesised that AQ total scores and subscale scores would be higher in adults who had attempted suicide more than once compared to adults who had attempted once. These hypotheses were tested using an independent samples t test, Mann-Whitney U tests, and binary logistic regression. Results: Most participants were female (83.3%, male = 12.9%, other = 3.8%), and ages ranged from 18 to 65 (median = 36.00; IQR = 19.00). Total AQ scores, as well as communication and imagination subscale scores were significantly higher in adults who had attempted suicide more than once compared to adults who had attempted suicide once. Even after removing participants with diagnosed or suspected autism (n = 34), 40.6% had an AQ score indicative of clinical concern (≥ 26). Conclusions: The findings suggest that high levels of autistic traits may frequently be present in adults who have attempted suicide, and that AQ scores are higher in those with a history of more than one suicide attempt. It may be possible to better identify suicide risk by screening autistic adults with mental health conditions for suicidal thoughts and behaviours, and by screening people with suicidal thoughts and/or behaviours for autism.