<p>The neutrophil-percentage-to-albumin ratio (NPAR) has emerged as a concise and effective biomarker for assessing systemic inflammatory status, with established prognostic value for mortality risk across various disease populations. This study aimed to elucidate the association between NPAR and both all-cause and cardiovascular mortality in patients with diabetes and prediabetes. A cohort of 8560 patients with diabetes and prediabetes was recruited from the National Health and Nutrition Examination Survey (NHANES), with mortality outcomes tracked through the National Death Index up to December 31, 2019. A weighted Cox regression model was used to evaluate the association of NPAR with all-cause and cardiovascular mortality. The restricted cubic spline (RCS) curve was used to assess the nonlinear relationship between NPAR and mortality outcomes. Subgroup analysis was conducted to evaluate the differences in the predictive performance of various NPAR features across different subgroups. Cox regression analysis indicated that participants in the highest quartile of NPAR exhibited a substantially increased risk of all-cause mortality (hazard ratio [HR] 1.54; 95% confidence interval [CI] 1.28–1.87) and cardiovascular death (HR 2.04; 95% CI 1.47–2.84) compared to the reference group. The RCS curve further illustrated a significant nonlinear correlation between NPAR and outcomes in patients with diabetes and prediabetes. NPAR can serve as a robust nonlinear predictor for both all-cause and cardiovascular mortality in individuals diagnosed with diabetes or prediabetes.</p>