A Baker’s cyst is an accumulation of fluid in the back (posterior) aspect of your knee. It denotes that something is wrong inside the joint, which is causing the production of the fluid. Often a Baker’s cyst is associated with a tear or injury to the meniscus, the cushion cartilage in the knee. It is important to find the cause of the swelling because swelling has what we call degradative enzymes in it--components that break down cartilage and tissue in the joint. Chronic swelling of the joint is not good for the joint surfaces; therefore, careful diagnosis and a treatment plan should be started. Physical therapy such as ice, soft-tissue massage, anti-inflammatory, and compression are good first steps for symptom relief. Aspiration of the cyst with a cortisone injection is sometimes helpful. Surgical repair of the underlying problem usually cures the cyst.