Aims/hypothesis <p>The aim of this study was to determine whether cardiac autonomic neuropathy (CAN) is an independent risk factor for kidney function decline in type 1 diabetes mellitus over a 15 year follow-up period.</p> Methods <p>Eighty seven participants with type 1 diabetes and eGFR &gt;30 ml/min per 1.73 m² underwent cardiovascular autonomic reflex testing at baseline. Renal data were retrieved at 4 year intervals over 15 years. Stratification of participants into Kidney Disease: Improving Global Outcomes (KDIGO) chronic kidney disease progression prognostic risk was done by using eGFR and urinary albumin/creatinine ratio (UACR). Longitudinal changes in eGFR and UACR were analysed using linear mixed-effects models with adjustment for potential confounders to determine whether CAN is an independent predictor of eGFR and UACR change over 15 years.</p> Results <p>At baseline, higher KDIGO risk category was associated with increased severity of CAN (<i>r</i>=0.38, <i>p</i>&lt;0.001) and increase in UACR (<i>p</i>&lt;0.001) compared with the lower risk group. Participants with established CAN at baseline exhibited greater mean (SD) eGFR decline of 14.8 (21.6) ml/min per 1.73 m², compared with 3.1 (7.3) and 3.3 (7.4) ml/min per 1.73 m² in the early stage and those without CAN (<i>p</i>=0.004). Mean (SD) increases in UACR were 0.4 (0.9), 11.3 (30.4) and 4 (8.9) mg/mmol for no CAN, early CAN and established CAN (<i>p</i>=0.03), respectively. After adjusting for potential confounders, baseline CAN was independently associated with both accelerated eGFR decline (<i>p</i>=0.018) and greater increases in UACR (<i>p</i>=0.002) over time.</p> Conclusions/interpretation <p>CAN is an independent predictor of both accelerated eGFR decline and increased albuminuria in type 1 diabetes. The study also explored the relationship between CAN and KDIGO prognostic risk in diabetic kidney disease, demonstrating that increased severity of CAN is associated with higher KDIGO prognostic risk.</p> Graphical Abstract <p></p>