OBJECTIVE: Type 1 diabetes is associated with increased prevalence of individual categories of mental disorders. We aimed to systematically synthesise the prevalence of all the different categories of mental disorders to estimate the overall burden of psychiatric morbidity in the type 1 diabetes population. METHOD: The electronic database of OVID was searched, and retrieved papers were screened for eligibility by two independent reviewers. Data were extracted using a standardised data extraction form and the quality of included papers was assessed. Where possible, comparisons with control groups without type 1 diabetes were made. Prevalence data were synthesised into Diagnostic and Statistical Manual of Mental Disorders version 5 categories, a narrative data-synthesis, and a subsequent meta-analysis where possible was conducted for mental disorder categories. RESULTS: Thirty-eight articles were included. Depressive, anxiety, and feeding and eating disorders were the most examined mental disorders. Studies utilising diagnostic interviews reported higher prevalence of mental disorders than in studies utilising clinical registers, with an up to 24-fold difference respectively. In studies with a control group, the prevalence for nearly every mental disorder were increased for the type 1 diabetes samples. CONCLUSIONS: There appears to be a high prevalence of mental disorders and associated need among people with type 1 diabetes, although the quality of research needs to improve. SYSTEMATIC REVIEW REGISTRATION: This protocol was submitted for registration with the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42020221530).