In 2005, 60 health care workers were recruited through services that attract injecting drug users (IDUs) and asked to complete attitude measures regarding IDU clients. Mediation analyses indicated that conservative health care workers displayed more negative attitudes toward their IDU clients because they believe that injecting drug use is within the control of the IDU. Negative attitudes toward IDU clients, in turn, were associated with worry about IDU clients' behavior in the clinic and with beliefs that IDU clients should disclose their hepatitis C status to their health care worker. Perceptions of controllability of drug use were also associated with the belief that IDU clients' ailments were caused by their IDU status. The study's limitations are noted.