Background <p>Sepsis is an organ dysfunction that impairs response to infection. Inflammatory biomarkers have been used to diagnose and monitor sepsis. The aim of the present study was to determine the role of immature granulocytes (IGs) in monitoring sepsis treatment.</p> Methods <p>This two-center, prospective, observational study included patients diagnosed with sepsis according to the Sepsis-3 criteria, who were followed-up in the adult intensive care units of the Bolu Izzet Baysal State Hospital and Bolu Izzet Baysal Training and Research Hospital (Bolu Merkez/Bolu, Türkiye). Laboratory investigation results, demographic information, treatment responses, and mortality were recorded. Patients were divided into 2 groups according to treatment: appropriate (group 1); and inappropriate (group 2). Differences in the number of IGs and IG% were compared. Differences with <i>P</i> &lt; 0.05 were considered to be statistically significant for all analyses.</p> Results <p>The study included 87 patients from 2 centers. The most common comorbidities were hypertension (54%) and 28-day mortality (37.9%). Empirical antibiotic therapy (43.7%) was appropriate for 38 patients (group 1) and 49 patients when the treatment was incorrect or inadequate (group 2). There were no significant differences between the groups in terms of laboratory investigation results on the day of treatment initiation. IG count and IG% on day 3 of treatment were significantly higher in group 2. Mortality was higher in patients with a high IG count (IG %) and in group 2.</p> Conclusion <p>IG% was a simple, inexpensive, and useful test for monitoring sepsis treatment and, in addition, IG count was also effective in predicting mortality.</p>