The Internet is a vital medium for communication, entertainment, and commerce, with more than 1 billion individuals connected worldwide. In addition to the many positive functions served by the Internet, it also has been used to facilitate the illicit sale of controlled substances. No-prescription websites (NPWs) offer--and then actually sell--controlled substances over the Internet without a valid prescription. NPW monitoring studies have focused primarily on the availability of prescription opioid medications, although many other drugs of abuse also are available online. Research indicates that these NPW sites are prevalent. Google or Yahoo searches simply using the term "Vicodin" return 40% to 50% NPWs in the top 100 sites. Thus, NPWs represent an important development in the sale of illicit drugs because of the ease with which controlled substances can be sold with relative anonymity. The emergence of NPWs requires new law enforcement and public health initiatives; continued monitoring efforts will determine whether efforts to reduce the availability of NPWs are successful.