Background: Asperger's syndrome in adulthood is frequently associated with depression, but few studies have explored the lifetime experience of self-reported suicidal ideation and suicide plans or attempts in this clinical group. We aimed to assess this prevalence in a clinical cohort of patients in the UK.

Method: In a clinical cohort study, we undertook a retrospective analysis of clinical survey data from adults newly diagnosed with Asperger's syndrome at a specialist diagnostic clinic between Jan 23, 2004, and July 8, 2013, in England. Patients completed a self-report questionnaire before clinical assessment, recording lifetime experience of depression, suicidal ideation, and suicide plans or attempts, along with self-reported measures of autistic traits and empathy. We compared the rate of suicidal ideation in the sample with published rates of suicidal ideation in the general population and other clinical groups. We also assessed associations between depression, autistic traits, empathy, and likelihood of suicidal ideation and suicide plans or attempts.

Findings: 374 adults (256 men and 118 women) were diagnosed with Asperger's syndrome in the study period. 243 (66%) of 367 respondents self-reported suicidal ideation, 127 (35%) of 365 respondents self-reported plans or attempts at suicide, and 116 (31%) of 368 respondents self-reported depression. Adults with Asperger's syndrome were significantly more likely to report lifetime experience of suicidal ideation than were individuals from a general UK population sample (odds ratio 9·6 [95% CI 7·6-11·9], p<0·0001), people with one, two, or more medical illnesses (p<0·0001), or people with psychotic illness (p=0·019). Compared with people diagnosed with Asperger's syndrome without depression, people with Asperger's syndrome and depression were more likely to report suicidal ideation (p<0·0001) and suicide plans or attempts (p<0·0001).

Interpretation: Our findings lend support to anecdotal reports of increased rates of suicidal ideation in adults with Asperger's syndrome, and depression as an important potential risk factor for suicidality in adults with this condition. Because adults with Asperger's syndrome often have many risk factors for secondary depression (eg, social isolation or exclusion, and unemployment), our findings emphasise the need for appropriate service planning and support to reduce risk in this clinical group.

Funding: The Three Guineas Trust, the Baily Thomas Foundation, the Medical Research Council, NIHR-CLAHRC-EoE, Cambridgeshire and Peterborough NHS Foundation Trust (CPFT), and the Autism Research Trust.