Background: Footprints of hominoids already demonstrated the existence of a plantar arch 3.7 million years ago, and, during human evolution, feet and not hands experienced extraordinary changes. The arch index is useful in determining the prevalence of pes planus and possibly predicting pathologic foot conditions, and it may serve as warning signs of structural and functional defects of the foot in a given population.Objective: The purpose of this study was to evaluate the plantar arch index using the staheli`s evaluation method and determined the point prevalence of pes planus and its association with sex difference, BMI, type of footwear and using footwear early in life.Method: This ex-post facto study involved 352 (150 males and 202 females) apparently health primary school pupils aged 8-12 years in southeast Nigeria who volunteered to participate in the study. The participants` biodata were obtained and their footprints collected with the ink method. Footprints were traced and selected foot dimensions measured on the footprints. Plantar arch index of each foot was calculated using the staheli`s formula; PI=A/B, where PI= plantar arch index, A= central region of the footprint and B= heel region of the footprint. Data collected were summarized and analysed with descriptive statistics of mean, standard deviation, percentage, chi-square and independent t-test, alpha level was set at 0.05Results: Mean age of participants was 10.28±1.26 while the mean body mass index was 17.60±2.81.The findings of this study revealed a low prevalence of pes planus (7.1%) in the population under study with males having slightly higher prevalence (4.3%) than females (2.8%). This study also found no significant association between sex difference and pes planus (p= 0.114), no significant association between type of footwear and pes planus (p= 0.314), but it found a significant association between BMI and pes planus (p= 0.039).The study also reveal that type of first footwear, type of frequent footwear, type of school footwear, type of home footwear and early footwear were not significantly associated with occurrence pes planus p=0.205, p=0.170, p=0.819, p=0.062 and p= 0.714 .Conclusion: The findings of this research shows that the prevalence of pes planus in the age group studied is not high and not of any health concern. Keywords: Staheli index, BMI, pes planus, footwears, pupils