Background and objectives Stroke, a leading cause of mortality and disability, involves significant inflammation both before and after onset. This study investigates the relationship between the aggregate index of systemic inflammation (AISI) and mortality in stroke patients. The objective is to determine if AISI, an easily accessible biomarker, can predict stroke prognosis. Materials and methods In this retrospective study, the medical records of patients who presented to Harran University Neurology Clinic between January 2018 and September 2023 were reviewed. A total of 200 patients, 106 of whom were diagnosed as having an ischaemic stroke and 94 of whom were diagnosed as having a haemorrhagic stroke, were included in the study. A control group was also formed, which consisted of 100 people of similar age and sex with the patient group. The controls had neither chronic disease nor chronic drug use. Using biochemical and full blood count parameters, neutrophil-to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), lymphocyte to monocyte ratio (LMR), monocyte to lymphocyte ratio (MLR), neutrophil to high-density cholesterol ratio (NHR), monocyte to high-density cholesterol ratio, systemic immune inflammation index (SII), systematic immune response index (SIRI) and the AISI were calculated for all patients and the control group. Results A comparison of the two groups revealed significantly higher NLR, NHR, PLR, LMR, MLR, SII, SIRI and AISI values compared with the controls. NLR, PLR, SII, SIRI and AISI values were significantly higher in haemorrhagic stroke than in ischaemic stroke. Elevated NLR level and SII were correlated to mortality (respectively p:0.000, p = 0.017). SIRI (p = 0.189) and AISI (p = 0.162) were not correlated to mortality. However, receiver operating characteristic curve analysis determined that mortality increased for patients with AISI values above 507.45 (p = 0.003). Conclusions The AISI was found to be high among stroke patients, especially in haemorrhagic strokes. A relationship was observed between the increase in AISI above a certain value and mortality. The AISI is an accessible biomarker that shows inflammation in stroke patients. Therefore, it can be used to predict the prognosis of stroke.