Based on the large number of small and medium-sized enterprises (SMEs) in the United States, their increasing interest in enterprise-wide software systems and their impact on the US economy, it is important to understand the determinants that can facilitate the successful implementation and assimilation of such technology into these firms' daily operations. The purpose of this study was to examine the impact of the top management team in SMEs that have adopted and implemented commercial open-source enterprise systems and to investigate the impact assimilation has on firm performance. Our results represent a significant contribution to understanding the use of open-source enterprise resource planning (ERP) software for SMEs, as these data are not publicly available. Findings suggest that (1) the information technology (IT) experience and knowledge of the team and the absorptive capacity of the SME play a significant role in the ability of the firm to assimilate open-source ERP systems, (2) assimilation mediates the role between customisation and operational performance and (3) the more aligned the open-source ERP system to the SME's business processes, the greater the opportunity to assimilate the technology and achieve higher levels of performance. (Contains 2 figures, 3 tables and 6 notes.)