Background: Sepsis is a major cause of mortality and morbidity worldwide, yet its diagnosis remains challenging due to non-specific clinical signs and the limitations of blood culture, which is time-consuming and has a significant false-negative rate. There is an urgent need for rapid, reliable biomarkers to facilitate early diagnosis. Objective: The current study aimed to evaluate the diagnostic utility of plasma D-dimer as a biomarker for neonatal sepsis and to compare its performance with C-reactive protein (CRP). Methods: A prospective case-control study was conducted in the Neonatal Intensive Care Unit of a private hospital during the period( January 2025 to March 2026. About 60 neonates were enrolled: 40 with clinical sepsis (sepsis group) and 20 healthy, matched controls. Plasma D-dimer were measured quantitatively using an automated latex-enhanced immunoturbidimetric assay. CRP and platelet counts were also assessed. ROC curve analysis was performed to determine diagnostic accuracy and the optimal D-dimer cutoff. Results: D-dimer levels were significantly higher in the sepsis group (4.5 µg/mL FEU) than in the control group (0.4 µg/mL FEU) (p<0.001). The ROC curve analysis showed excellent diagnostic accuracy for D-dimer, with an AUC of 0.93 (95% CI: 0.87–0.99), comparable to CRP (AUC = 0.91). The sensitivity, specificity, positive predictive value and negative predictive value of D-dimer were 90.0%, 85.0%, 92.3%, 81.0%, respectively. As a result, the optimal cutoff value was 1.15 µg/mL FEU. Subgroup analysis showed significantly higher D-dimer levels in culture-positive sepsis than in culture-negative clinical sepsis (p=0.012). Conclusion: Plasma D-dimer is a very.