Emergence of extensively drug-resistant tuberculosis (XDR-TB) is a global public health concern. To examine the epidemiology and clinical course of XDR-TB, Shah and colleagues analyzed TB cases that were reported in the United States from 1993 to 2007. The authors report risk factors, clinical features, and survival rates for XDR-TB compared with multidrug-resistant TB and drug-susceptible TB cases. Among the authors' findings is that 83 cases of XDR-TB have occurred in the United States since 1993. Recent declines in annual cases parallel improvements in TB and HIV/AIDS control.