Spontaneous bacterial peritonitis (SBP) is a severe complication of liver cirrhosis whose diagnosis is based on a polymorphonuclear leukocyte (PMN) value >250 mm 3 , yet this PMN value cannot identify all existing types. The aim of our study was to determine the clinical and biological factors that were associated with SBP and predict its occurrence, focusing on the neutrophil-to-lymphocyte ratio (NLR) as one of them. Our retrospective study included 216 patients with liver cirrhosis who were hospitalized between December 2019 and January 2010 at the Emergency County Clinical Hospital of 'St. Apostle Andrew' in Constanta, Romania. Demographic, clinical, and laboratory data were collected from patient observation sheets. The patients were divided into two groups: One group of patients with SBP and the other without SBP. The diagnosis of SBP was made when patients presented with PMN >250 mm 3 and other causes of secondary bacterial peritonitis were excluded. The mean age of the patients was 61.25±10.67 years, and the alcoholic etiology of liver cirrhosis was most common (44%). Univariate logistic regression analysis showed that there was an association between biological parameters, such as serum white blood cells, total platelet count, total bilirubin, serum albumin, international normalized ratio, creatinine, erythrocyte sedimentation rate (ESR), serum sodium, alkaline reserve, and NLR, and clinical parameters, such us upper gastrointestinal bleeding and cardiac comorbidities in the occurrence of SBP. Multivariate analysis identified ESR and NLR as predictive factors in the occurrence of SBP. The area under the curve (AUC) was 0.916 [P<0.001, 95% confidence interval (CI) 0.870-0.949] for ESR and AUC was 0.963 (P<0.001, 95% CI 0.928-0.984) for NLR, respectively. In conclusion, the combination of these 2 biological parameters is useful in identifying or excluding SBP.