There is little bulk clinical evidence on nutritional status and mortality in patients with diabetes. The purpose of this study was to examine the relationship between prognostic nutritional index (PNI) and all-cause mortality and cardiovascular mortality in adults with diabetes.This study included 5916 adult patients with diabetes from the National Health and Nutrition Examination Survey 1999-2018. Cox proportional risk models were used to estimate risk ratios (HRs) and 95% CIs for all-cause mortality, cardiovascular disease (CVD) mortality.During a mean follow-up of 8.17 years, there were 1248 deaths from all causes and 370 deaths from CVD. After multivariate adjustment, the risk of all-cause mortality was reduced by 24%, 38%, and 28% in Q2 (49.0-52.99), Q3 (53.0-57.99), and Q4 (≥58.0), respectively, compared with Q1 (PNI<49.0). The risk of cardiovascular mortality was reduced by 30%, 27%, and 26%, respectively. Consistent results were observed in the subgroup analysis.Lower serum PNI levels were significantly associated with higher all-cause and CVD mortality. These findings suggest that maintaining an appropriate range of serum PNI status may reduce the risk of death in patients with diabetes.© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.