An outbreak of infections due to Mycobacterium fortuitum associated with electromyography (EMG) is described. During a 6-week period, six patients who received EMG at one facility developed soft-tissue infections manifested by slowly expanding suppurative nodules at sites of needle electrode insertion. M. fortuitum was isolated from five patients; four isolates that were evaluated further were M. fortuitum biovariant fortuitum. EMG procedures were done in one laboratory by one physician and assistant. Standard procedures included use of reusable needle electrodes disinfected with 2% glutaraldehyde and then rinsed with tap water. On recognition of the outbreak, the procedure was changed to include autoclaving of needle electrodes. Active surveillance for 1 year revealed no further cases. M. fortuitum could not be isolated from the laboratory, EMG equipment and reagents, or skin of the medical personnel. The outbreak demonstrates that nontuberculous mycobacterial infection may be associated with EMG.