Introduction The association between type 1 diabetes (T1D) and other auto-immune diseases is well known. However, a quantitative overview of all associated auto-immune diseases and their prevalence in T1D is lacking. Methods We searched PubMed, Web of Science, EMBASE and Cochrane library in September 2018 to identify relevant articles about the prevalence of the following associated auto-immune diseases in T1D cohorts: auto-immune thyroid disease, celiac disease, gastric autoimmunity including

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... ernicious anemia, vitiligo and adrenal gland insufficiency. A meta-analysis was performed to estimate pooled prevalence using a random-effects model. Furthermore, random-effects meta-regression analysis was performed to assess the association between prevalence and mean age or diabetes duration. Results One hundred eighty articles were eligible including a total of 293 889 type 1 diabetes patients. Hypothyroidism (65 studies) was prevalent in 9.8% (95% CI: 7.5–12.3) of patients. Meta-regression showed that for every 10-year age increase, hypothyroidism prevalence increased 4.6% (95% CI: 2.6–6.6, P < 0.000, 54 studies). Weighted prevalence of celiac disease was 4.5% (95% CI: 4.0–5.5, 87 studies). Gastric autoimmunity was found in 4.3% of patients (95% CI: 1.6–8.2, 8 studies) and vitiligo in 2.4% (95% CI: 1.2–3.9, 14 studies) of patients. The prevalence of adrenal insufficiency was 0.2% (95% CI: 0.0–0.4, 14 studies) and hyperthyroidism was found in 1.3 percent (95% CI: 0.9–1.8, 45 studies) of type 1 diabetes patients. For all analyses, statistical heterogeneity between studies was moderate to high. Conclusions The prevalence of antibody-mediated auto-immune disease is high among type 1 diabetes patients. Especially hypothyroidism and celiac disease are frequently found.