Background: Attention-deficit/hyperactivity disorder (ADHD) is a common developmental disorder, often persisting into adulthood. Whilst medication is first-line treatment for ADHD, there is a need for evidence-based non-pharmacological treatment options for adults with ADHD who are either still experiencing significant symptoms or for those who have made the informed choice not to start medication. Methods: We systematically searched PsycINFO, MEDLINE (Ovid), EMBASE, CINAHL and CENTRAL for randomised controlled trials of non-pharmacological treatments for ADHD in adults. After screening of titles and abstracts, full text articles were reviewed, data extracted, and bias assessed using a study proforma. Results: There were 32 eligible studies with the largest number of studies assessing cognitive behavioural therapy (CBT). CBT consisted of either group, internet or individual therapy. Conclusions: The majority found an improvement in ADHD symptoms with CBT treatment. Additionally, mindfulness and cognitive remediation have evidence as effective interventions for the core symptoms of ADHD and there is evidence for the use of group dialectical behavioural therapy and hypnotherapy. However, the evidence for these is weaker due to small numbers of participants and limitations due to lack of suitable control conditions, and a high risk of bias.