The South African government has benefited to date from information technology in many ways. The importance of understanding and influencing South African citizens’ acceptance of E-Government services is critical, given the substantial investment in government communication, information system technology and the potential for cost saving. One of the most successful E-Government initiatives, the electronic filing system (eFiling), allows tax returns to be filed electronically. Despite many taxpayers adopting this method, a large number are still using the traditional manual method of filing tax returns. This study utilised the decomposed theory of planned behaviour with factors adjusted specifically for South Africa as a developing country to identify the possible determinants of user acceptance of the eFiling system among taxpayers. This exploratory study was conducted by means of a questionnaire survey. For taxpayers using the manual method, lack of facilitating conditions such as access to computer and internet resources was the most significant barrier to eFiling usage, while taxpayers using the electronic method reported perceived usefulness as the primary determinant in their decision to use eFiling. Understanding these acceptance factors can extend our knowledge of taxpayers’ decision-making and lead to better planning and implementation of future E-Government initiatives in South Africa and other developing countries.