Attention-deficit/hyperactivity disorder (ADHD) often co-occurs with substance use (SU) and/or substance use disorder (SUD). Individuals with concurrent ADHD and SU/SUD can have complex presentations that may complicate diagnosis and treatment. This can be further complicated by the context in which services are delivered. Also, when working with young people and adults with co-existing ADHD and SU/SUD, there is uncertainty among healthcare practitioners on how best to meet their needs. In February 2022, the United Kingdom ADHD Partnership hosted a meeting attended by multidisciplinary experts to address these issues. Following presentations providing attendees with an overview of the literature, group discussions were held synthesizing research evidence and clinical experience. Topics included: (1) A review of substances and reasons for use/misuse; (2) identification, assessment and treatment of illicit SU/SUD in young people and adults with ADHD presenting in community services; and (3) identification, assessment and treatment of ADHD in adults presenting in SU/SUD community and inpatient services. Dis-cussions highlighted inter-service barriers and fragmentation of care. It was concluded that a multimodal and multi-agency approach is needed. The consensus group generated a table of practice recommendations providing guidance on: identification and assessment; pharmacological and psychological treatment; and multi-agency interventions.