The term flat foot is surrounded by confusion and there is little to help the clinician to identify cases which require treatment and to avoid treating many children unnecessarily. Research for 25 years has been aimed at elucidating this problem by identifying and evaluating a series of signs and tests. These tests allow the recognition of the abnormal foot as early as possible, when efficient treatment is likely to be most effective. The results indicate that evaluation of the flat foot should be based on a combination of signs, with most emphasis on the result of the great toe extension test.