Background: People with intellectual disabilities are more likely to have diabetes and develop complications from it. Diabetes management is complex and insulin treatment in particular, people with intellectual disabilities may require additional support that is not always available. This review aimed to identify barriers and facilitators to managing diabetes with insulin in adults with intellectual disabilities. Method: Patient and public involvement (PPI) was integral to the development of the research question. A systemised review was conducted across CINAHL, the British Nursing Index and MEDLINE. PRISMA guidelines were followed. Narrative synthesis of the evidence was undertaken. Results: Barriers and facilitators to managing diabetes with insulin in people with intellectual disabilities were identified related to the individual, other people participating in their care, and broader environmental and social factors. Conclusions: People with intellectual disabilities who use insulin, require reasonable adjustments to education, support, and a person-centred approach to facilitate supported self-management. More training for their supporters is needed and further inclusive research with PPI is recommended.