Full Text Article. Also available at: https://onlinelibrary.wiley.com/doi/abs/10.1002/j.1681-4835.2014.tb00455.xDefaulter tracing systems are patient centred information systems which are used to enhance monitoring of patients who have dropped out of health programs. The aim of this study is to explore the operation of defaulter tracing systems in practice. The study has been undertaken in Tanzanian health facilities by using qualitative data collection methods. Activity theory is employed as a conceptual framework to analyze the findings. Findings show that the implementation of defaulter tracing system is challenged by issues of the existing information systems, such as absence of clear guidelines and tools, and information recording incompleteness, as well as contextual issues. The paper contributes to Healthcare Information System literature (HIS) which has elaborated how patient centred information systems are utilized in practice at the level of primary health care. This study concludes by providing implications for policy, practice, design and implementation.