We reviewed a rare breast infection occurring 4 months after nipple piercing. Clinical examination suggested carcinoma. Mycobacterium fortuitum was eventually isolated after surgical biopsy and debridement. Antibiotic therapy was initiated intravenously using two drugs and oral therapy was continued for 6 months. A contralateral mycobacterial lesion emerged and was excised along with a residual fibrotic nodule at the original biopsy site. When adequate sampling of a complex and suspicious breast mass is benign and initial bacterial cultures are sterile, mycobacterial infection should be considered, particularly when there is a history of previous nipple piercing procedures.