The prevalence of self-reported suicidal ideation, suicide attempts and non-suicidal self-injury (NSSI) remains unclear among adults with autism unrecognised in childhood who attend psychiatric services.

We aimed to estimate the prevalence of suicidal ideation, suicide attempts and NSSI; identify factors associated with suicide attempts and NSSI; and describe NSSI in this group.

Sixty-three new patients at an adult psychiatric out-patient clinic (57% women, mean age 32 years) who met full (n = 52) or subthreshold (two A criteria and minimum of two B criteria; n = 11) DSM-5 criteria for autism spectrum disorder were included in the study. Clinical assessments included overall diagnostic review, Paykel's questions on passive and active suicidality, evaluation of NSSI with the Functional Assessment of Self-Mutilation, and results of cognitive tests. One follow-up of medical records was made.

In this sample of psychiatric out-patients identified as first having autism in adulthood, almost a third (31%) of patients reported suicidal ideation during the past month, 86% had lifetime suicidal ideation and 25% reported at least one suicide attempt. Factors associated with suicide attempts included hazardous or harmful alcohol use and/or drug-related problems, and severity of depression. A total of 44% reported NSSI. Factors associated with NSSI were female sex, history of suicidal plans and antisocial personality disorder. Substance or alcohol use were often overlooked, especially in women.

Suicidal ideation, suicide attempts and NSSI were very common in adults with autism who were recently referred to an out-patient psychiatric service. Suicidal ideation and NSSI were more common than suicide attempts. Clinicians should always consider suicidal ideation and NSSI in adult psychiatric patients with autism.