During 1995-1996, staff from the California departments of corrections and health services and local health departments investigated two outbreaks of drug-susceptible tuberculosis (TB). The outbreaks occurred in two state correctional institutions with dedicated HIV housing units. In each outbreak, all cases were linked by IS6110-based DNA fingerprinting of Mycobacterium tuberculosis isolates. This report describes the investigations of both outbreaks; the findings indicated that M. tuberculosis can spread rapidly among HIV-infected inmates and be transmitted to their visitors and prison employees, with secondary spread to the community.