Osteoarthritis (OA) is the most common form of arthritis in older patients, causing pain that can significantly reduce function and quality of life. OA is classified as either primary or secondary disease, depending on the underlying etiology. Causes of secondary OA include trauma, other joint disease, and metabolic conditions. Diagnosis is based on patient history, physical examination, and radiographic findings. The mainstay of treatment is the use of nonsteroidal anti-inflammatory agents; NSAIDs that can be given once or twice daily increase patient compliance. Other therapeutic measures include exercise programs and--in patients with severe pain and limited function--surgical intervention.