ADHD is common in psychiatric populations. This study aimed to compare clinical characteristics in adults with and without ADHD who presented with self-harm, and to compare later risk of suicidal behaviour within 6 months. Eight hundred four adults presented with self-harm (with and without suicidal intent) at psychiatric emergency services at three Swedish hospitals. Persons with a discharge ICD-10 diagnosis F90.0-F90.9 or a prescription for ADHD medication were considered to have ADHD (n = 93). Medical records were reviewed for evidence of subsequent suicide attempts (SA) within 6 months; suicides were identified by national register. Recent relationship problems were more prevalent in the ADHD group. While the index episodes of those with ADHD were more often non-suicidal, and actual SAs more often rated as impulsive, medical lethality at presentation did not differ in attempters with and without ADHD. Subsequent SAs (fatal or non-fatal) were observed in 29% of the ADHD group and 20% in all others (P = .005). A logistic regression model showed elevated risk of suicidal behaviour during follow-up in the ADHD group (OR = 1.70, CI 1.05–2.76), although a final regression model suggested that this association was partly explained by age and comorbid emotionally unstable personality disorder. Findings highlight the need for clinicians to take self-harm seriously in adults with ADHD.