Objective: Acute bronchiolitis, primarily caused by Respiratory syncytial virus (RSV), is the most common cause of hospitalization in young children. Despite international guidelines supporting clinical diagnosis, laboratory evaluations are often conducted with limited validity. We aim to evaluate the association between C-reactive protein (CRP) levels at admission and disease severity in children hospitalized due to RSV bronchiolitis. Study design: This single center retrospective cohort study included children (0-24 months old) who were hospitalized due to RSV bronchiolitis (January 2018 – March 2022) with CRP levels taken upon admission. Clinical data and severity parameters were extracted using MD-clone platform and the clinical research unit at SUMC. Results: 1,874 children (mean age of 6.7 months, 59% males) with a median CRP level of 1.92mg/dL were included. Children with elevated CRP (>1.92mg/dL) were significantly older (5.1 vs. 3.8 months, p<0.001), had higher rates of pneumonia (9.4% vs. 4.3%, p<0.001 ), urinary tract infection (UTI), (2.2% vs. 0.2%, p<0.001), acute otitis media (AOM), (1.7% vs 0.2%, p<0.001), admissions to pediatric intensive care unit (PICU) (7.4% vs 3.7%, p<0.001), antibiotic treatment (49.8% vs 37.2%, p<0.001) and longer hospitalizations (3.83 vs 3.31 days, p=0.001). Multivariable analysis predicted increased risk for UTI, PICU admission, pneumonia, and longer hospitalization (relative risk of 11.6, 2.25, 1.98, 1.44, respectively, p<0.001)). CRP thresholds of 3.51, 1.9, and 2.81 mg/dL for PICU admission, UTI, and pneumonia, were calculated using Youden’s index with AUC of 0.72, 0.62, and 0.61, respectively. Conclusions: Elevated CRP levels at admission are associated with increased disease severity and higher complication rates in children hospitalized with RSV bronchiolitis.