This study was undertaken to determine the number of patients who started anti-TB treatment at the TB Centre in Addis Ababa, but never completed a full regular course for one year. There were 460 or 6 percent of all the TB patients that were treated for the disease in this period. The reasons for treatment failure were analyzed. Although the commonest cause of default was clinical improvement before completion of therapy, many of the reasons related to the socio-economic situation and cultural background in Ethiopia. Despite defaulting, there was sputum conversion to negative in 85 percent of these cases, which is a good result for unsupervised TB chemotherapy, in a country such as Ethiopia.