There is controversy concerning the definition and measurement of the medial longitudinal arch of the foot. Various techniques are reported to assess the medial arch height, including radiographic measurements and footprint analysis, which are the most commonly used methods. Some authors define footprint analysis as unreliable for measuring the arch height. The purpose of this study was to investigate the relationship between radiologically measured angles and the arch index obtained from footprint analyses in 38 children with flexible pes planus. A positive correlation of arch index was found between lateral talo-horizontal and lateral tale-first metatarsal angles (p < 0.05). These angles have been used by some authors to describe the height of the medial longitudinal arch of the foot. This study demonstrated that footprint analysis could be used effectively for screening studies and at individual office examinations.