Over the last decade, drug sales through cryptomarkets located on the so-called darknet have received increasing attention. This paper considers how web surveys might be used to provide insights concerning those people who purchase drugs on cryptomarkets. First, it analyses data from the European Web Survey on Drugs (EWSD), with a view to identifying differences between respondents who buy drugs on cryptomarkets and those who acquire drugs from other sources. The study shows that people using cryptomarkets as a usual source of supply were a small group of users in most participating countries, but that proportions differ significantly, and that buyers were more likely to be male and consume more substances on average. Second, the sampling of web survey respondents on the darknet is discussed based on a sampling strategy tested in Austria, highlighting the challenges and opportunities involved in undertaking survey recruitment on the darknet. The paper highlights the importance of building trust, establishing credibility and guaranteeing anonymity, since awareness of privacy issues is seemingly higher among darknet users than surface web users. By doing so, the authors shows how people who buy drugs on cryptomarkets might be reached to improve their representation in future web surveys for drug data collection.