Thirty current and former crack users aged 16-24 years participated in a qualitative study about their crack use and related behaviours. The study investigates the process of marginalization (social relations, sources of income and health situation) before and after the start of crack use. Results show that because many crack users were raised in a problematic home situation and have little education, they were already in a marginal position before they started using crack. However, the use of crack accelerated the process of marginalization, because they experienced a shrinking social network that developed around other users, and because they performed illegal activities to buy crack. As result, many users spent time in prison. Regarding health, they experienced respiratory problems, deteriorating physical fitness, paranoia and heart palpitations. Furthermore, homelessness and crack use are intertwined.