The atypical, or nontuberculous, mycobacteria are opportunistic pathogens that usually cause infection following accidental trauma or surgery. These organisms are ubiquitous in nature but have been found with increasing frequency in other environments that include medical offices and surgical suites. Management of atypical mycobacterial ocular infections can be difficult because in vitro antibiotic activity does not always correlate with in vivo efficacy and because normal immune defenses against mycobacteria may work too slowly to prevent irreversible damage to infected ocular tissues. This report describes a patient who developed a severe ocular infection due to Mycobacterium chelonae after vitrectomy. Despite eradication of the infection, the eye became blind and painful. Arch Ophthalmol. 2000;118:1125-1128