BACKGROUND Acute respiratory infections remain a leading cause of morbidity and mortality in Sierra Leone; however, similar to other African countries, little is known regarding the contribution of influenza. Routine influenza surveillance is thus a key element to improve understanding of the burden of acute respiratory infections in Africa. In 2011, the World Health Organization (WHO) funded the Strengthening Influenza Sentinel Surveillance in Africa (SISA) project with the goal of developing and strengthening influenza surveillance in eight countries in sub-Saharan Africa, including Sierra Leone. This paper describes the process of establishing a functional Influenza Sentinel Surveillance (ISS) system in Sierra Leone, a post-conflict resource-poor country previously lacking an influenza monitoring system. METHODS Sierra Leone utilized a systematic approach, including situational assessment, selection of sentinel sites, preparation of implementation plan, adaptation of the standard operating procedures, supervision and training of staff, and monitoring of influenza surveillance activities. The methods used in Sierra Leone were adapted to its specific context, using the Integrated Disease Surveillance and Response (IDSR) strategy as a platform for establishing ISS. RESULTS The ISS system started functioning in August 2011 with subsequent capacity to contribute surveillance activity data to global influenza databases, FluID and FluNet, demonstrating a functional influenza surveillance system in Sierra Leone within the period of the WHO SISA project support. Several factors were necessary for successful implementation, including a systematic approach, national ownership, appropriate timing and external support. CONCLUSIONS The WHO SISA project demonstrated the feasibility of building a functional influenza surveillance system in Sierra Leone, integrated into existing national IDSR system. The ISS system, if sustained long-term, would provide valuable data to determine epidemiological and virological patterns and seasonal trends to assess the influenza disease burden that will ultimately guide national control strategies.