Ultraviolet (UV) light exposure can cause both erythema and conjunctivitis.(1) High intensity discharge (HID) lamps (e.g., those used in industrial lighting) can emit UV radiation if the envelope surrounding the bulb is damaged or absent. These lamps can continue to function despite this damage, creating the potential for uncommon routes of exposure to actinic UV radiation (UV-B and UV-C).(2,3) Food and Drug Administration (FDA) regulations require that mercury vapor and metal halide lamps contain labeling that alerts consumers to possible "serious skin burn and eye inflammation from shortwave UV radiation if the outer envelope of the lamp is broken or punctured."(4, p. 658) Although non-self-extinguishing lamps (Type R lamps) were involved in these incidents, self-extinguishing lamps (Type T lamps) are also available. FDA regulations require that these lamps extinguish within 15 min after the outer envelope is broken or punctured.(4) Regulations also require that all incidents involving injury associated with the use of metal halide or mercury bulbs be reported to the light bulb manufacturer, who is obligated to report to the FDA. It is important to retain any broken bulb to identify bulb type and manufacturer. This investigation followed the occurrence of adverse health events during an indoor gymnasium sporting event. Results from the environmental investigations, the case-patient questionnaires, and the medical literature support the hypothesis that the majority of health symptoms reported by persons in attendance at the sporting event were a result of overexposure to UV radiation from damaged metal halide lamps. Multiple incidents of unintentional human exposure to UV light from damaged mercury vapor lamps and germicidal light bulbs have been reported.(5-8) However, previous reports lacked quantitative UV measurements that could be used to directly calculate a dose-response relationship. In this case study we present an incident of erythema and conjunctivitis in a school setting resulting from damaged metal halide lamps emitting UV light. On February 1 and 2, 2002, the Occupational and Environmental Epidemiology Branch at the North Carolina Division of Public Health received multiple reports of skin and eye burns from 13 persons who had attended or participated in a basketball tournament held in a school gymnasium. School maintenance staff reported a broken bulb, which raised suspicion regarding possible UV radiation exposure as the cause of the symptoms.