Patient traumatized posterior aspect of upper arm, near shoulder, while "scratching" the area by rubbing on the tiles of a swimming pool. The minor abrasion healed without incident, but three months later slowly developed an enlarging, firm, slightly tender bright red plaque (as shown). A biopsy showed granuloma. Tissue culture eventually grew M. marinum. The patient was successfully treated with oral minocycline along with adjunctive thermotherapy.