Few large-scale multicenter data on additional immune phenomena in patients with type-1 diabetes are available. The DPV initiative aggregates standardized anonymized patient records for quality control and epidemiologic research. This report includes data on 23 837 patients with type-1 diabetes, age <30 years and at least 1 antibody measurement, from 242 specialized centers from Germany and Austria (8012 patients <12 years, 12 866 1218 years and 2959 patients 1830 years). At least one B-cell-antibody (ICA, GAD, IA2, IAA at onset) was present in 10 133 patients. B-cell-AB-negative patients were significantly younger at diabetes onset (8.4 versus 9.1 years, P<0.0001). 2459 patients (10.3%) had positive thyroid antibodies (TAK, TPO) with female predominance (62%, P<0.0001) and association to older age and longer duration of diabetes (both P<0.0001), but no difference with age at onset. Thyroid-autoimmunity was not associated with positivity for any B-cell-AB, however the number of B-cell-AB+s detected was slightly higher in patients with thyroid autoimmunity (1.8 versus 1.6, P<0.0001). Antibodies suggestive of celiac disease (tTG, gliadin IgG/IgA or endomysium) were present in 3923 patients, with a significantly younger age at onset (7.5 versus 8.2 years, P<0.0001). Parietal cell antibodies were found in 244 patients, again associated with older age (15.9 versus 14.1 years, P<0.001). Adrenal antibodies were found in 71 patients, this group did not differ clinically from patients without adrenal antibodies. In 352 patients (61% female, mean age 14.6 years), at least 3 different autoimmune phenomena were present, and 4 organ systems were involved in 33 patients. In conclusion, Thyroid autoimmunity is the most prevalent additional immune phenomenon in type-1 diabetes, especially in adolescent and young adult women. Parietal or adrenal antibodies are rare. B-cell-autoimmunity is not a predictor for additional autoimmune phenomena in type-1 diabetes.