"Loss to follow up" is a major problem for national tuberculosis (TB) programs worldwide. Loss to follow up is operationally defined as an inability to find a TB patient during the course of their TB treatment (6-24 months). In some cases up to one quarter of TB patients are lost. Typically, national TB programs do not have the resources to follow up such patients. There are no systematic reviews describing this problem, nor what can be done to prevent it. Therefore this project will comprise a systematic review to look at the scope of loss to follow up and the measures that can be put in place to prevent it. Given the global interest in TB elimination (a goal of the Sustainable Development Goals) this project is likely to be of international interest.