Introduction:To estimate the incidence of Reactive Thrombocytosis among febrile young infants and to assess the utility of platelet count as a potential predictor and diagnostic tool of serious bacterial infection (SBI). Methods and Materials:This study was conducted as a prospective non-randomized study between March 2016 to Feb 2018 at the tertiary care pediatric unit, Srinagar, India. Inclusion criteria were all infants 30 to 89 days of age, admitted with rectal temperature>38?C/100.4?F without an apparent focus of infection on history and clinical examination. Exclusion criteria were infants having fever more than 72 hours and who had received antibiotics or vaccination within 48 hours of presentation. Also, the results of the sepsis evaluation on admission were recorded. SBI included all cases of occult bacteremia, urinary tract infection, bacterial meningitis, pneumonia, bacterial gastroenteritis and infections of the soft tissues and bones. Results:Of the 298 infants studied, 78 (26.2%) had SBI. Platelet count was significantly higher in infants with SBI compared to those without {Platelet count ≥ 4 lakhs /mm3 in SBI (84.6%) vs. Non-SBI (42.4%).Mean platelet count 5.1 ? 1.1 in SBI vs. 3.9 ? 1.6 in Non-SBI which was statistically significant (P<0.05). Thrombocytosis had a moderate ability in predicting SBI [Area under curve area under the curve: 0.760]. The combination of platelet count ≥450,000/mm3, WBC ≥15,000/mm3, C-reactive protein ≥2 mg/dl and pyuria ≥5 White blood cells (WBC) per High power field (HPF) resulted in misclassification of only 2 infants with SBI (5.1% of SBIs). Conclusions:Reactive thrombocytosis was a frequent finding in young infants with SBI. Thrombocytosis ≥450,000 cells/mm3, in combination with leukocytosis, elevated C-reactive protein (CRP) and pyuria, may help in early recognition of febrile young infants at risk for SBI.