The study focused on the sociodemographic characteristics of homeless drug users in Rotterdam and whether they differed from housed drug users, the nature of their living conditions, the reasons for being homeless, and whether the period of homelessness was a factor in the motivation to change one's lifestyle. The study involved a literature review, interviews with key persons, field notes from community fieldworkers, a survey of drug users (n=204), and photographic reports from 6 homeless drug users. The data were obtained in 1998/1999. The urban-ethnographical research method includes the subculture theory. The subculture theory describes how, once excluded from regular society, people find a new home in the marginal subculture of, in the case at issue, the world of the homeless. The longer someone is homeless, the more attached they become to this new social environment; and once embedded in the subculture, they find it increasingly difficult to find their way back to regular society. This study found that among the homeless drug users compared with the housed drug users, there were more women, more ex-offenders, and more foreigners. Further, the homeless group used heroin and cocaine on more days than the housed drug users. A large proportion of the homeless drug users had no identity papers and no health insurance. This did not, however, lead to more self-reported sickness or a higher prevalence of infectious diseases compared with non-homeless drug users. Easily accessible (low threshold) social care centers and assistance were important. Few of the homeless had voluntarily chosen a homeless life; most described an event that triggered their homelessness. The average duration of homelessness was 17 months. The longer someone had been homeless, the less inclined they were to change their situation. This latter finding suggests that intervention should occur as early as possible in the period of homelessness. Knowledge about problems of marginally housed drug users who are at risk of becoming homeless will assist in planning appropriate help for this group. 7 figures and 42 references