In the early 1990s, some persons in New York City were diagnosed with a new, virtually untreatable form of tuberculosis. Called Strain W, it very rapidly killed 80–90% of those infected: most died within 4 months. All of the drugs routinely used to treat tuberculosis were useless. Strain W has now spread to at least 10 states and to France. By 1996 it accounted for one-quarter of the drug-resistant tuberculosis cases in the United States. This virulent outbreak demonstrates how multidrug-resistant tuberculosis is transforming treatment and control of the disease.