Cutaneous infections with Mycobacterium marinum are rare. They also are known as swimming pool or fish tank granulomas. Often the history of contact with contaminated water associated with microtrauma of the upper extremities leads to the correct diagnosis. Since chlorination of swimming pools has become standard, cases of swimming pool granuloma have become rare. Contact with fish tanks now is the most common route of infection. Positive culture of skin biopsy leads to the correct diagnosis. Moxifloxacin in combination with other antibiotics is often effective.