Traditional herbal medicines encompass an extremely diverse group of preparations that originate from many different cultures. In recent years, such products have become widely available commercially in developed countries, where mixtures prepared from medicinal plants have been marketed or uses that were never contemplated in the traditional healing systems from which they emerged. In many countries, herbal medicines are not subject to rigorous standards with respect to manufacturing, efficacy, quality and safety. For example, herbal remedies containing plant species of the genus Aristolochia and used in Europe for body weight loss have caused kidney disease and urothelial cancers and are now classified as carcinogenic to humans. This monograph evaluates the carcinogenic risks to humans posed by the use of some traditional herbal medicines, Fumonisin B1, and the industrial organic chemicals naphthalene and styrene, and provides an update of the data on the carcinogenicity of aflatoxins. An Annex to the volume describes fungal sources and formation of aflatoxins in foods and feeds, and discusses practical strategies for reduction of aflatoxin levels.