In Asia, patients increasingly seek tuberculosis (TB) treatment in the private sector; however, few private sector practices follow international TB management guidelines. We conducted a study to measure the frequency and predictors of seeking TB diagnosis in the private sector among 756 HIV-infected TB patients in four Thai provinces during 2005-2006. Of enrolled patients, 97 (13%) first sought care at a private provider and 83 (11%) at a pharmacy. In multivariable analysis, the only factor independently associated with seeking care at a private provider was having a high TB stigma score. Factors independently associated with seeking care at a pharmacy included not knowing that TB can be cured and that TB care can be provided close to home. Patients reported that the most influential factor in choosing a provider was confidentiality (468; 62%). Further research is needed to evaluate whether educating the community about the confidentiality, availability, and success of curing TB at government health facilities can promote prompt utilization of public TB treatment services by HIV-infected patients in Thailand.