Nosocomial outbreaks and pseudo-outbreaks caused by the nontuberculous mycobacteria (NTM) have been recognized for more than 20 years and continue to be a problem. Most of these outbreaks have involved the rapidly growing mycobacterial species Mycobacterium fortuitum and M. abscessus. The reservoir for these outbreaks is generally municipal and (often separate) hospital water supplies. These mycobacterial species and others are incredibly hardy, able to grow in municipal and distilled water, thrive at temperatures of 45 degrees C or above (M. xenopi and M. avium complex), and resist the activity of organomercurials, chlorine, 2% concentrations of formaldehyde and alkaline glutaraldehyde, and other commonly used disinfectants. Disease outbreaks usually involve sternal wound infections, plastic surgery wound infections, or postinjection abscesses. Pseudo-outbreaks most commonly relate to contaminated bronchoscopes and endoscopic cleaning machines (M. abscessus) and contaminated hospital water supplies (M. xenopi). Knowledge of the reservoir of these species, their great survival capabilities within the hospital, and newer molecular techniques for strain comparison have helped control and more quickly identify current nosocomial outbreaks or pseudo-outbreaks caused by the NTM.