Background Idiopathic flexible flatfoot in children most frequently improves with age and remains asymptomatic.It is a physiological variation of the normality that does not require treatment unless it becomes symptomatic.The aim of this research was to investigate the reason why some individuals with flexible flatfoot become symptomatic by analysis of the differences in the relative alignment of each segment of the foot between symptomatic and asymptomatic patients with idiopathic flexible flatfoot using radiographic measurements.Methods One hundred patients with idiopathic flexible flatfoot were retrospectively identified and divided into two groups:asymptomatic (n=50) and symptomatic (n=50).Standing anteroposterior and lateral radiographs of the foot were analyzed.Five measurements were calculated to describe the alignment of the foot.An independent-samples t-test and Logistic regression test were used for statistical analysis.Results Age and sex were similar in the two groups.The independent-samples test revealed significant differences in two parameters:the anteroposterior talonavicular coverage angle and the lateral talo-first metatarsal angle.When the Logistic regression test was performed,only the talonavicular coverage angle showed statistical significance.Conclusions The lateral displacement of the navicular bone,measured by the anteroposterior talonavicular coverage angle,seems to be related to the onset of symptoms.In individuals with otherwise normal flexible flatfoot,an increase in this angle might be an important risk factor for developing symptoms.