Introduction: Adult acquired flatfoot is a common cause of foot pain. The majority of series describe surgery although important non-surgical series exist. This series of 166 patients gives an overview of the clinical spectrum of the condition and outcomes. Materials and Methods: Data was collected prospectively on 166 consecutive patients with adult acquired flatfoot between 1995 and 2005. 104 patients were reviewed at a median of eight years (range 3–13). A standardised clinical examination, AOFAS hindfoot and visual analogue satisfaction scores were performed. Results: There were 40 men (median age 56 years) and 126 women (median age 60 years). 68% had other musculoskeletal problems. Patients were Truro staged at presentation; Stage 1: 26 patients. Stage 2A: 84 patients. Stage 2B: 25 patients. Stage 2C: 23 patients. Stage 3: 6 patients. Stage 4: 2 patients. Stage 1 patients were younger (p<0.001). 133 patients had soft-tissue symptoms, but 33 had degenerative problems. Degenerative patients had a higher median age (p=0.0138) and stiffer deformities (p<0.0001). Most patients (131, 78.9%) were managed conservatively. Surgery was commoner in the arthritic group (p=0.001). Fifty-two conservatively treated feet were clinically reassessed. In 31 (59%) patients the Truro stage had not changed, 11 (21%) had improved and 10 (20%) had deteriorated. Twenty percent of patients treated with orthoses stopped using them after 18 to 24 months. In non-surgically treated patients, the median AOFAS score was 73/100 and satisfaction score 71/100. In surgically treated patients the median AOFAS score was 74/100 and satisfaction score 83/100. Discussion: There is a young group of patients with adult acquired flatfoot, with soft tissue symptoms but no progressive deformity. There is a large group with a flexible deformity who can mostly be treated with orthoses, and an older group with stiffer, arthritic deformities who are more likely to need surgery. Conclusion: Final outcomes and satisfaction were similar in surgically and non-surgically treated patients.