Mycobacterium marinum is the etiologic agent of fish tank granuloma. The clinical course is usually benign: spontaneous healing is possible within weeks or months. However, fish tank granuloma is sometimes resistant to several antibiotics. We report a case of M. marinum infection of a finger in a 73-year-old cook. The disease was resistant to a number of antibiotics and required the amputation. The history of this patient testifies that M. marinum can be resistant to several antibiotics and that skin infections can be sometimes so severe as to require the amputation of a finger.