Ischial bursitis is the painful inflammation or swelling of a fluid-filled sac (bursa) that separates the buttocks muscle from the underlying bone. It is usually caused by sitting on hard surfaces for prolonged periods of time, running, cycling or direct trauma to the buttocks region. Treatment involves rest, application of ice to the area of tenderness and the use of nonsteroidal anti-inflammatory medication. Gentle stretching may also help resolve painful symptoms. In severe cases, removal of bursal fluid or the bursa itself may be indicated.