E-mail is an efficient communication tool, but at the same time it is an efficient vehicle for Internet pollution in the form of spam—unsolicited, bulk e-mailings. Spam is a global phenomenon, and debate about possible means of controlling it is lively. Spammers impose a negative externality on users. The volume of spam-type e-mail sent is above the social optimum and thus produces dead-weight. To solve the spam problem and evaluate spam-control measures, one needs to measure the disutility experienced by e-mail users who receive spam. The current study employs conjoint analysis of stated-preference data to estimate e-mail users' overall inconvenience cost attributable to spam. The results show the inconvenience cost of spam to be about 3.067 won (US$ 0.0026) per spam message.