Beginning in 1990, outbreaks of multidrug-resistant tuberculosis (MDR-TB) have been reported in hospitals and prisons in the eastern United States (1). During June 1991-January 1995, MDR-TB was diagnosed in 47 patients and one health-care worker at a 120-bed, infectious disease referral hospital in urban Madrid; on April 19, 1995, the Spanish Field Epidemiology Training Program was asked to investigate this outbreak. This report summarizes the findings of this investigation, which suggested that nosocomial transmission of MDR-TB occurred on a hospital ward for patients with human immunodeficiency virus (HIV) infection.