Black carbon is a good indicator of combustion-related air pollution, and was only recently recognized as a short-lived climate-forcer, which contributes to warming the Earth's atmosphere.This report presents the results of a systematic review of evidence of the health effects of black carbon in ambient air. Epidemiological studies provide sufficient evidence of the association of cardiopulmonary morbidity and mortality with exposure to black carbon. Toxicological studies suggest that black carbon may operate as a universal carrier of a wide variety of chemicals of varying toxicity to the human body. Although black carbon may not be a major, directly toxic component of fine particulate matter, reducing peoples exposure to particulate matter containing black carbon should reduce its effects on their health, as well as helping to mitigate climate change.This review is of particular interest to environmental health professionals concerned with assessing and reducing the health effects of air pollution, as well as to those who use scientific evidence in support of climate change mitigation policies.