**Abstract**

Loss to follow-up (LTFU) is a serious issue in the field of tuberculosis (TB) since it can lead to TB outbreaks and drug resistance. The proportion of LTFU patients differs among different countries, regions, year, and institutions. In some countries, the number of patients that were LTFU nearly reaches half of the total patients. Underlying factors such as age, gender, education, residence, financial factors, migration, and social stigma are discussed in this chapter. These factors should always be taken into consideration whenever a treatment program is designed. Suggestions have been made regarding some interventions that could potentially solve the problem of LTFU. With these points in mind, an ambitious approach should be taken to reduce the number of LTFU patients up to zero.

**Keywords:** tuberculosis, TB, loss to follow-up, LTFU, default
