A 1974 article reporting the existence of angiosarcoma of the liver among polyvinyl-chloride workers in a single factory in Kentucky is reprinted, followed by a contemporary editorial note. The original article reports the diagnosis of angiosarcoma of the liver between 1967 and 1973 in four men employed in the polyvinyl-chloride polymerization section of a factory. All of the men had worked continuously in the section for at least 14 years prior to onset of illness, and all worked directly in the polymerization process. Because only approximately 25 cases of angiosarcoma of the liver occur annually in the United States, four cases at a single factory was highly unusual, and the 1974 publication raised the possibility of the presence of a work related carcinogen, possibly vinyl- chloride (75014). Epidemiologic studies were being started to gather data on the occurrence of angiosarcoma among workers at other vinyl-chloride factories. The 1997 editorial note discussed the vinyl-chloride/angiosarcoma connection as an example of the concept of the sentinel health event. The 1974 report was cited as the first recognition of the carcinogenicity to humans of vinyl-chloride monomer. The 1974 publication and a related journal article stimulated a series of clinical investigations, epidemiologic studies, and toxicologic analyses, ultimately identifying vinyl- chloride as a highly potent chemical carcinogen. The recognition of the carcinogenicity of vinyl-chloride resulted in the OSHA reducing the exposure standard for vinyl-chloride gas from 500 parts per million (ppm) to 1ppm. The editorial concludes that this episode underscores the importance of informed clinical observation in the recognition of work related illness.