Serum CXCL‐10 levels were significantly higher in patients with acute‐onset type 1 diabetes or slowly progressive type 1 diabetes, irrespective of the co‐occurrence of AITD, than in non‐diabetic controls (acute‐onset type 1 diabetes with AITD, n = 7: 166.7 ± 81.6 pg/mL; acute‐onset type 1 diabetes without AITD, n = 20: 125.9 ± 62.5 pg/mL; slowly progressive type 1 diabetes with AITD, n = 8: 206.3 ± 140.0 pg/mL; slowly progressive type 1 diabetes without AITD, n = 15: 160.2 ± 83.5 pg/mL vs non‐diabetic controls: 49.1 ± 11.5 pg/mL, all P < 0.001). This evidence concerns the gene CXCL10 and type 1 diabetes mellitus.