Thirty-seven cases of rapidly growing mycobacterial wound infections following augmentation mammaplasty were identified between 1979 and 1988. The infections were usually unilateral and had a narrow geographic distribution: almost 60% were from Texas and 92% from five southern coastal states. In Texas a seasonal incidence was observed; 45% of all previously reported and current patients had undergone mammaplasty in April, May, or June. Although these findings suggested a possible common source, analysis of 35 available isolates revealed 19 different phenotype patterns. Five different taxonomic groups were represented, although most isolates (70%) were Mycobacterium fortuitum biovar fortuitum. Plasmid bands were identified in 10 of 15 strains studied, with nine different profiles. An additional 11 cases of breast infection due to rapidly growing mycobacteria not associated with augmentation were also identified, of which nine came from the same states that contributed mammaplasty cases. Rapidly growing mycobacterial infections of the breast are endemic in Texas and other southern coastal states, and the heterogeneity of the isolates suggests that most cases are unrelated.