A total of 125 sex workers completed both a face-to-face structured questionnaire and a qualitative taped interview. All participants had been involved in both sex work and drug use. The mean age of the 92 female and 33 male participants was 26.7 years. The participants reported higher levels of drug use than were found among respondents in the British Crime Survey who reported drug use. Differences were particularly significant for crack cocaine, heroin, and nonprescribed methadone. Seventy-eight percent of the most vulnerable sex workers had received services from their local authority. Most worked "outdoors" or as "independent drifters." The most vulnerable sex workers were all girls who had been involved in prostitution before age 18. They were chronic drug users, often needing funds from prostitution to pay for their drug use. They had also been "pimped" and/or supported at least one boyfriend's drug use. The nonvulnerable sex workers were all over 18 and were independent, business-oriented, and positive about their sex work. None of these participants reported a current drug problem, and they believed they would have no problem in stopping sex work or any drug use if they chose to do so. The most important factors in stopping sex work and drug use were the separation of private from commercial sex and not having problematic drug use as the primary motivation for sex work. This study recommends that statutory and voluntary agencies work in partnership to identify youth at risk of entering prostitution. Further, law enforcement efforts should give high priority to arresting and prosecuting persons who seek paid sex with children. 3 tables and 6 references