Résumé : Background In 2010, the government of Sierra Leone implemented the Free Health Care Initiative (FHCI) in the country with the objective of reducing the high maternal, infant, and child mortality rates and improving general health indicators. The objective of this study was to assess the trends in the prevalence of health care-seeking and to identify the determinants of healthcare service utilization by caregivers of children younger than five years. Methods The analysis of health-care-seeking behavior was done using data from four populationbased surveys in Sierra Leone before (2008) and after (2013, 2016, 2019) the FHCI was implemented. Care-seeking behavior was assessed with regard to caregivers seeking care for children under-five in the two weeks prior to each survey. We compared the percentages of healthcare-seeking behavior change and identify factors associated with healthcareseeking using a modified Poisson regression model with generalized estimating equations. Results In 2008, a total of 1208 children with fever were recorded, compared with 2823 children in 2013, 1633 in 2016, and 1464 in 2019. Care-seeking for children with fever was lowest in 2008 (51%; 95% CI (46.4-55.5)) than in 2013 (71.5%; 95% CI (68.4-74.5)), 2016 (70.3%; 95% CI (66.6-73.8)), and 2019 (74.6%; 95% CI (71.6-77.3)) (p < 0.001). Care-seeking in 2013, 2016 and 2019 was at least 1.4 time higher than in 2008 (p < 0.001) after adjusting for mother's age, wealth, religion, education level, household head and the child's age. Careseeking was lowest for children older than 12 months, mothers older than 35 years, children living in the poorest households, and in the northern region. A trend was observed for the sex of the household head. The level of care-seeking was lowest when the household head was a man. Conclusions The increase in healthcare-seeking for children under-five with fever followed the introduction of the FHCI in Sierra Leone. Care-seeking for fever varied by the child's age, caregiver's age, household wealth, the sex of the household head and region. Maintaining the FHCI with adequate strategies to address other barriers beyond financial ones is essential to reduce disparities between age groups, regions and, households.