Mycobacterium marinum is an environmental opportunistic mycobacterium that usually causes superficial skin infections or invasive infections caused by having an open wound exposed to contaminated water. We report here the case of a 50-year-old female who developed tenosynovitis of the hand caused by M. marinum. She presented to the hospital with a 4-month history of right hand swelling and the other previous 2 weeks she developed purulent lesions of the same hand. She was treated with incision and drainage. A routine culture grew out acid -fast bacilli and polymerase chain reaction testing revealed M. marinum. She was given rifampin and clarithromycin for 8 months. The hand healed well without residuals. This case demonstrates that M. marinum can present as tenosynovitis. We also reviewed the literature.