BACKGROUND Mycobacterium fortuitum is a rapidly growing group of nontuberculous mycobacteria more common in patients with genetic or acquired causes of immune deficiency. There have been few published reports of Mycobacterium fortuitum associated with breast infections mainly associated with breast implant and reconstructive surgery. METHODS We report a case of a 51-year-old Caucasian woman who presented to our one-stop breast clinic with a two-week history of left breast swelling and tenderness. Following triple assessment and subsequent incision and drainage of a breast abscess, the patient was diagnosed with Mycobacterium fortuitum and treated with antibiotic therapy and surgical debridement. CONCLUSIONS This is a rare case of a spontaneous breast abscess secondary to Mycobacterium fortuitum infection. Recommended treatment is long-term antibacterial therapy and surgical debridement for extensive infection or when implants are involved.