Since the U.S. Congress passed the Dietary Supplement Health and Education Act (DSHEA) in 1994, herbal products, including herbal dietary supplements, represent the fastest growing segment of the vitamin, mineral supplements, and herbal products industry. To ensure consumer health protection, the quality and safety of raw herbal plants used for dietary supplement preparations have to be determined. To date, safety issues concerning the hepatotoxic and tumorigenic ingredients in many raw herbs and herbal dietary products are quite limited. Pyrrolizidine alkaloids are a class of hepatotoxic and tumorigenic phytochemicals present in more than 6000 plants and have been detected in herbal plants and dietary supplements. In this review, the human exposure, metabolic activation leading to hepatototoxicity and tumorigenicity of the pyrrolizidine alkaloid-containing Chinese herbal plants, and analytical methods used to identify and quantify pyrrolizidine alkaloids in herbal plants and commercial samples are discussed. Suggestions for future research are provided.