Periarticular cysts in the shoulder joint are relatively rare. The most common are paralabral cysts, which can cause suprascapular nerve entrapment syndrome. Acromioclavicular juxtaarticular cysts have been described in association with full-thickness rotator cuff tears and a degenerated acromioclavicular joint. Intramuscular cysts of the rotator cuff are a relatively rare and unknown type of periarticular cyst. We report a case of an intramuscular cyst of the rotator cuff that was associated with a tear of the rotator cuff.