In this research, we aimed to investigate the predictive value of the systemic immune inflammation index and prognostic nutritional index on mortality among patients with an endoprosthesis after a hip fracture. In this retrospective, cross-sectional study, a total of 915 patient files applied to our hospital between 2020 and 2023 with an endoprosthesis after a hip fracture were subjected to the study. The patients were divided into 2 groups: alive (n = 396; 43.3%) and deceased (n = 519; 56.7%). The eosinophil-to-lymphocyte ratio, hemoglobin-to-red cell distribution width ratio (HRR), mean platelet volume-to-platelet ratio (MPVPR), neutrophil-to-lymphocyte ratio, monocyte/lymphocyte ratio, platelet-to-lymphocyte ratio, MPV-to-lymphocyte ratio, monocyte-to-eosinophil ratio (MER), neutrophile-to-monocyte ratio, systemic inflammation index (SII), and prognostic nutritional index (PNI) parameters of the patients were evaluated. The mortality rate was higher among male patients, with a statistically significant difference (P < .05). The follow-up duration, albumin, HGB, eosinophil, lymphocyte, eosinophil %, eosinophil-to-lymphocyte ratio, HRR, and PNI means were significantly higher in the living group (P < .05). Age, MPV, MPVPR, neutrophil-to-lymphocyte ratio, monocyte/lymphocyte ratio, platelet-to-lymphocyte ratio, MPV-to-lymphocyte ratio, MER, and systemic inflammation index were significantly higher in the deceased group (P < .05). The predictive value of gender (B = −0.362; P < .01), age (B = 0.036; P < .01), HRR (B = −1.100; P < .01), MPVPR (B = 8.209; P < .01), MER (B = 0.006; P < .01), and PNI (B = −0.078; P < .01) were statistically significant at the multivariate level. The time of death was significantly predicted by gender (B = 0.10; P < .05), age (B = −0.02; P < 0 = 1), HRR (B = 0.61; P < .01), MPVPR (r = −4.16; P < .01), MER (B = −0.01; P < .05), and PNI (B = 0.03; P < .01). The predictive value of PNI for the 30-day mortality rate was statistically significant (AUC: 0.643; P < .01). For a PNI cutoff value of 34.475, sensitivity was 69.7%, and specificity was 51.1%. The PNI has predictive value both in estimating overall mortality and in predicting the 30-day mortality rates among patients undergoing endoprosthesis after a hip fracture.