The purpose of our study was to identify the cause of symptomatic ankle arthritis in a consecutive series of patients presenting in a tertiary care setting. Between 1991 and 2004, 639 patients with Kellgren grade 3 or 4 ankle arthritis presented to the University of Iowa Orthopaedic Foot and Ankle Surgery service. The cause of the arthritis was determined based on medical history, physical examination, and imaging studies. To get a sense of the relative prevalence of the etiologies of lower extremity arthritis in our setting, we evaluated the cause of arthritis of all new patients presenting to the University of Iowa Orthopaedic Department from 1999-2004 with arthritis of the ankle, to those with arthritis of the hip or knee during one year. Of the 639 arthritic ankles, 445 (70%) were post-traumatic, 76 (12%) were rheumatoid disease and 46 (7%) were idiopathic (primary osteoarthritis). The post-traumatic ankle arthritis patients were most commonly associated with past rotational ankle fractures. The majority of ankle arthritis is associated with previous trauma, whereas the primary cause of knee or hip arthritis is idiopathic. Unique strategies to prevent or treat post-traumatic ankle arthritis are needed.