There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers. Am. J. Ind. Med. 55:395–411, 2012. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.