Between January 1 and May 15, 1988, foot infections due to Mycobacterium chelonae subspecies abscessus were diagnosed in eight persons who had undergone invasive procedures at a podiatry office. A cohort study was performed to evaluate risk factors for disease. Persons who underwent procedures before 10:30 AM were more likely to have developed infection than those with procedures after that time (relative risk, 5.6). In addition, procedures involving any of the second through fourth toes were more likely to have resulted in infection than procedures involving only the first and/or fifth toes (relative risk, 4.4). Persons with 0, 1, or 2 risk factors had attack rates of 5%, 14%, and 60%, respectively. Mycobacterium chelonae subspecies abscessus organisms of the same antimicrobial resistance pattern as the patients' strains were cultured from distilled water in a reusable, nonsterilized container. A jet injector used to administer lidocaine was held between procedures in a mixture of the distilled water and a disinfectant as recommended by the manufacturer. Inoculation of patients with mycobacteria by the jet injector may have only occurred early in the day due to slow killing of the bacteria by the disinfectant. The outbreak emphasizes the pathogenicity of this water-associated organism and the need for high-level disinfection of jet injectors.