Introduction: Birthweight is a critical public health indicator with low birthweight (LBW) associated with adverse neonatal outcomes and chronic diseases. In Sri Lanka, determinants of birthweight in term neonates, particularly distinguishing LBW and small for gestational age (SGA) from foetal growth restriction (FGR) remain understudied. Objective: To describe the composition and determinants of birthweight in term neonates at a tertiary care centre. Methods: A descriptive cross-sectional study was conducted at university neonatal unit of Colombo North Teaching Hospital, Sri Lanka. 437 live, term (>37weeks) singleton new-borns were recruited. The prevalences of LBW , SGA, and FGR were determined. Associations of LBW , SGA and FGR were analysed using the chi-square test. Results: Mean birthweight was 2916(±408)g. Prevalence of LBW , SGA and FGR were 14.0%(n=61), 15.1%(n=66), and 14.9%(n=65), respectively . Among 61 LBW neonates, 46(75.4%) were SGA, and 31(50.8%) had FGR. Significant risk factors for LBW were female sex (OR:0.42;p=0.002), maternal underweight (OR:2.37;p=0.026), anaemia at delivery (OR:2.06;p=0.025), and history of stillbirths (OR:6.34;p=0.037). Risk factors for SGA and FGR were maternal underweight (p