An outbreak of postinjection abscesses occurred in Barranquilla, Colombia, and was associated with local injections of lidocaine given in a single physician's office. Over a 5-month period, 350 (18%) of approximately 2,000 injected patients developed localized cutaneous abscesses or cellulitis; of 210 abscess specimens that were cultured, 205 were positive for rapidly growing mycobacteria, subsequently identified as Mycobacterium abscessus. The source of the outbreak was not identified. M. abscessus could not be characterized by pulsed-field gel electrophoresis, but all isolates were identical in terms of drug and heavy metal resistance patterns and random amplified polymorphic DNA PCR profiles. We believe this is the first report of the use of this latter technique for investigation of an outbreak due to M. abscessus. Therapy with a combination of surgical excision and 3-6 months' administration of clarithromycin was successful for 95% of 148 patients treated in this manner; in contrast, therapy was successful for less than one-third of patients treated with surgery alone or clarithromycin alone. This is the largest of the nine known outbreaks of postinjection abscesses that have occurred due to rapidly growing mycobacteria and is the first in which an effective method of therapy was demonstrated.