Background: Although the prevalence of tuberculosis has decreased significantly over the past decades, the certain populations with mental illness are at increased risk for tuberculosis infection and transmission. However, no studies have examined the performance of different laboratory examination methods among people with severe mental illness in China. Methods: In this study, we firstly performed a retrospective study to evaluate the feasibility of three routine laboratory methods, including sputum microscopy, solid culture and GeneXpert, to diagnose tuberculosis patients with mental illness. Results: During August 2010 and March 2013, a total of 251 TB patients based on clinical and radiographic criteria with severe mental illness were enrolled in this study. The majority of patients was homeless (97/251, 38.6%), and the other 62 (24.7%) and 92 (36.7%) were from urban and rural region, respectively. The most frequently diagnosed mental illness was schizophrenia, accounting for 84.1% (211/251) of patients available for analysis. In addition, the laboratory received 753 sputum samples collected from these 251 TB patients, of which 76.0% (572/753) of samples were classified as salivary sputum, which were unqualified for microscopy and culture. When the test results were analyzed by patients, the positive numbers of TB patients detected by sputum microscopy, solid culture and GeneXpert were 3 (1.2%), 5 (2.0%) and 5 (2.0%), respectively. Conclusions: In conclusion, our findings reveal that the current laboratory examinations based on sputum samples seem not to be suitable for the diagnosis of active TB in the persons with severe mental illness. The products using a non-invasive specimen such as urine deserve further evaluation, which may generate benefit for the early diagnosis of TB in this special population.