The New York City Fire Department (FDNY) is the largest fire department in the United States, with over 11,000 firefighters. In 1994, FDNY changed to a modern firefighting protective uniform. The major difference between traditional and modern uniforms is that modern uniforms include both protective over-coat and over-pant, whereas traditional uniforms include only the over-coat. Furthermore, modern uniforms are manufactured using improved thermal protective textiles that meet or exceed current National Fire Protection Association standards for structural firefighting. The purpose of this study was to determine the impact of the modern uniform on the incidence and severity of FDNY burn injuries. We also evaluated the incidence and severity of other non-burn injuries to determine whether there was serious adverse impact. The number of lower-extremity burns decreased by 85% when 2 years' experience while wearing the modern uniform was compared with 2 years while wearing the traditional uniform. Upper-extremity burns and head burns decreased by 65% and 40%, respectively. Severity indicators (days lost to medical leave, hospital admissions, and skin grafts) for lower- and upper-extremity burn injuries were all substantially reduced. This occurred without significant change in the incidence or severity of trunk burns, heat exhaustion, inhalation injuries (actually decreased), or cardiac events. The reduction in the incidence and severity of burn injuries, the major occupational injury affecting this workforce, has been so dramatic and without untoward effects that the introduction of the modern uniform must be characterized as a sentinel event in the history of firefighter health and safety.