Background and Aims: Ventilator-associated pneumonia (VAP) is the most common healthcare-associated infection in adult critical care units. The reason behind the different levels of severity and the outcome in different individuals is not established yet.Co-morbidities and age may be a valid reason.In an attempt to find out the reason behind the different levels of severity of VAP in different individuals, we conducted a studywith the primary objective being to assess the quantitative correlation between the colony forming units (CFU) of Acinetobacter baumannii in the endotracheal tube aspirate and the Clinical Pulmonary Infection Score (CPIS) in mechanically ventilated patients without co-morbidities. The secondary objective was to see whether the severity of VAP depends on the number of CFU(>10 5 /ml). Methods: This observational study was conducted in a 27-bedded intensive care unit of a tertiary care hospital in northern India. Endotracheal tube aspirate was collected from patients with suspected VAP.A total of 81 patients without any prior co-morbidity and having Acinetobacter baumannii in their endotracheal tube aspirate were included in the study group. Quantification of Acinetobacter baumannii was done by counting CFU.The CPIS was calculated for all Acinetobacter baumannii positive patients. Correlation between CFU of Acinetobacter baumannii and CPIS was assessed using Spearman's Rho correlation coefficient. Results: Among 81 patients having Acinetobacter baumannii infection, only 61.9% had a CPIS >4. There was an insignificant correlation between the quantity of CFUs of Acinetobacter baumannii and CPIS ( P value = 0.784). Conclusion: Number of CFU >10 5 /ml in an endotracheal tube aspirate culture bears no relation to the severity of VAP as predicted by the CPIS.