The objective index as developed by Qaura, Deodhar, and Jit, in 1980 was used to estimate the incidence of flat foot (pes planus) in 990 school pupils (532 females and 458 males) between the ages of 5 and 14 years. The ratio of contact area to the total area of the middle of the footprint (contact index 1) (4/10), usually measured with a planimeter, is accepted as the true representative of the condition of arches. In this field study, contact index II (ratio of contact width to the total width of the foot) which is simple, reliable, and correlates with contact index I has been used to assess flat foot. The mean for the contact index and standard deviation have been calculated. Feet have been considered as normal up to 1 SD around the mean value of the index and values greater or lesser than this have been considered abnormal. Furthermore, mean +/- 1 SD to 2 SD has been considered as possible flat foot, whereas mean +/- 3 SD and above has been taken as definite flat foot. On the whole, bilateral flat foot is not common among children of school age in Port Harcourt (0.60%). It is, however, more common in females (0.75%) than males (0.44%). Unilateral flat foot (2.22%) is found to be more common than bilateral flat foot. Early introduction to the use of shoes may predispose to flat foot. We were not in a position to say if any of the subjects found with flat foot would have a painful foot.(ABSTRACT TRUNCATED AT 250 WORDS)