How long it takes for TB to transform into obsolete TB depends on the severity of the patient’s disease and the strength of the immune system and varies from person to person. Obsolete tuberculosis is defined as a condition in which the diseased area has been completely killed by the binding bacilli, the inflammation is eliminated, and the destroyed lung tissue is replaced by surrounding fibrous or calcified deposits, which appear as a striated shadow or calcified nodular shadow on CT of the lung and do not show changes on long-term follow-up. Tuberculosis patients with mild disease and strong patient’s autoimmunity may have old tuberculosis foci detected directly during physical examination; patients with severe disease and low immunity may need long-term anti-tuberculosis treatment after, for example, about 6-8 months of treatment to gradually transform into old tuberculosis. In addition, because tuberculosis is contagious, patients with tuberculosis should take regular, adequate, full course and combined anti-tuberculosis treatment, while paying attention to isolation to avoid infection and regular reexamination.